U.S. equities failed to hold earlier gains on Wednesday as investors digested President Donald Trump's outline for tax reform, while earnings season continued.

The Dow Jones industrial average closed lower after rising as much as 74.78 points, with Procter & Gamble contributing the most losses. The 30-stock index held about 1 percent away from its all-time high of 21,169.11, however.

The S&P 500 also fell slightly after flirting with an all-time high, with real estate leading decliners. The Nasdaq composite notched an all-time high earlier in the session, but finished marginally in the red.

"The discussion around the tax plan is a positive for the market," said John Conlon, chief investment officer at People's United Wealth Management. But "I don't think the market is excited; I think it takes some pressure off the market, but there are still questions about some of the details."

Major indexes intraday

Source: FactSet

Expectations for lower corporate taxes have been a boon for stocks ever since Trump was elected in November. The S&P has gained 11.6 percent since the election and was on track to post a weekly gain of nearly 2 percent on reignited hopes around lower taxes.

Top White House officials outlined President Donald Trump 's tax plan Wednesday, a proposal they said would be the "biggest tax cut" in U.S. history. The proposal slashes the corporate tax rate to 15 percent from 35 percent.

The White House added there will be a "one-time tax" on the trillions of dollars held by corporations overseas. However, Treasury Secretary Steven Mnuchin said the rate for that tax has yet to be determined.

Retail stocks popped on the announcement, as it revealed Trump's plan did not include a border adjustment tax. The SPDR S&P Retail ETF (XRT) rose 1 percent.

It's time for the administration to "go big or go home and a 15% corporate tax rate will certainly make that happen," said Peter Boockvar, chief market analyst at The Lindsey Group, in a note to clients.

"I'll leave it to others to figure out if and how we get there (will obviously be tough) but the implications will have to also be measured by any change in interest rates in response in gauging the impact on corporate earnings and for other obligations," he said.

Trump will also be outlining his tax reform vision ahead of a potential government shutdown. Government funding will end Friday unless Congress can agree on at least a temporary funding resolution.

"I think some of the hesitancy in the market has to do with the potential government shutdown later this week," said Randy Frederick, vice president of trading and derivatives at Charles Schwab.

"There's no historical precedent" for a market downturn during a government shutdown, he said. "But because the Trump presidency is different from any we've ever had, there's going to be some hesitancy."

Meanwhile, earnings season carried on, with PepsiCo, United Technologies, Procter & Gamble and Twitter all posted a better-than-expected profit. Twitter's stock popped about 8 percent after reporting.

This earnings season has shown thus far that Corporate America did very well last quarter. Of the 181 S&P 500 components that had reported as of Wednesday, 77 percent had topped earnings expectations while 67 percent beat on the top line, according to data from The Earnings Scout.

"Remember though solid 1Q 2017 results only confirm what has already happened in the markets! 1Q 2017 results should not be used to infer what is going to happen," said Nick Raich, CEO of The Earnings Scout, in a note. "For that information, look to the direction of 2Q 2017 EPS estimate revisions."

He said that second-quarter earnings growth expectations have fallen every week this earnings season since March 22.

There were no major economic data reports released Wednesday, but Wall Street looked ahead to Friday's first-quarter GDP report.

"What concerns me is the Fed is raising rates in a modest economy with earnings growing modestly," said Phil Blancato, CEO of Ladenburg Thalmann Asset Management. "The rate of change in the economy is changing. The consumer is healthy but not necessarily spending money."

The Dow Jones industrial average (Dow Jones Global Indexes: .DJI) fell 21.03 points, or 0.1 percent, to close at 20,975.09, with Procter & Gamble leading decliners and Verizon the top advancer.

The S&P 500 (INDEX: .SPX) slipped 1.16 points, or 0.05 percent, to end at 2,387.45, with real estate leading seven sectors lower and telecommunications outperforming.

The Nasdaq (NASDAQ: .IXIC) fell 0.27 points to close at 6,025.23.

About four stocks advanced for every three decliners at the New York Stock exchange, with an exchange volume of 963.03 million and a composite volume of 4.065 billion at the close.

The CBOE Volatility Index (VIX) (STOXX: .VIX), widely considered the best gauge of fear in the market, traded near 10.8.

—CNBC's Jacob Pramuk contributed to this report.

On tap this week:

Thursday

Earnings: Alphabet, Microsoft, Intel, Amazon.com, Raytheon, Baidu, Starbucks, Expedia, Comcast, Bristol-Myers Squibb, Flex, GoPro, Western Digital, Vertex , Sirius XM Radio, Under Armour, American Airlines, Southwest Air, MGM Growth, Generac, Domino's Pizza, CME Group, KKR, Johnson Controls, Union Pacific, UPS, Total, Celgene, Deutsche Bank, Alexion Pharma, Nintendo, AbbVie, Bayer, Air Products

7:45 a.m. ECB rate decision

8:30 a.m. ECB President Mario Draghi press briefing

8:30 a.m. Jobless claims

8:30 a.m. Durable goods

8:30 a.m. Advance econ indicators

10:00 a.m. Pending home sales

10:00 a.m. Housing vacancies

Friday

Earnings: Exxon Mobil, Chevron, Colgate-Palmolive, Honda Motor, Barclays, UBS, Sony, Synchrony Financial, Spirit Airlines, Autoliv, Sanofi, Spirit Airlines, Goodyear Tire, Calpine, Cabot Oil and Gas, Phillips 66, Weyerhaeuser

8:30 a.m. Q1 adv Real GDP

9:45 a.m. Chicago PMI

10:00 a.m. Consumer sentiment

2:30 p.m. Philadelphia Fed President Patrick Harker

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