Berkshire said about $29.11bn of its net income was attributable to the reduction of the United States corporate tax rate from 35 per cent to 21 per cent.
Buffett said a "purchasing frenzy" binge by deal-hungry chief executives employing cheap debt has made that task hard.
Berkshire's cash pile swelled to $116 billion from $109 billion in the third quarter.
The insurance businesses reported an underwriting loss of $2.2 billion as hurricanes and other natural disasters in 2017 weighed on results, leading to the first annual underwriting loss after a 14-year streak of gains, Buffett said in the letter.
"Our smiles will broaden when we have redeployed Berkshire's excess funds into more productive assets", Buffett wrote.
Buffett went on to extol Berkshire's investing methods.
It was also short on faulting excesses of Wall Street and Washington, and said nothing about Berkshire's plan to create a healthcare company with Amazon.com Inc and JPMorgan Chase & Co.
It's important to remember that even Buffett's Berkshire Hathaway (BRK-A, BRK-B) hasn't been immune to significant swings in its stock price either.
Both are considered candidates to eventually replace Buffett, 87, as Berkshire's chief executive.
Neither has signaled any intention of stepping down soon, though Berkshire last month named two additional vice chairmen who could eventually succeed Buffett as chief executive. "Each has been with Berkshire for decades, and Berkshire's blood flows through their veins".
Berkshire Hathaway wholly owns dozens of companies - from Dairy Queen to Duracell - and holds significant shares in large and diverse corporations including American Express, Apple, Bank of America, Charter Communications, Coca-Cola, Delta Air Lines, General Motors, Goldman Sachs, Moody's, Wells Fargo and Southwest Airlines.
The investment company run by Warren Buffett made $44.9 billion of earnings attributable to shareholders during the year, but warned that changes to the way changes in valuation were booked for its $170 billion of tradable stocks would make comparisons "useless" in future.
Buffett supported President Trump's Democratic rival, Hillary Clinton, during the 2016 election.
"Often, high-grade bonds in an investment portfolio increase its risk", he wrote.