The yen crept higher to 108.47 per dollar.
The biggest winners were the Australian and New Zealand dollars, which soared as shorts scrambled to exit their positions. Traders said some had bet on a more hawkish Fed outlook.
"The Fed was not as optimistic as people thought, and that is consistent with a lower U.S. dollar and the fall in bond yields that we saw," said Commonwealth Bank of Australia analyst Joe Capurso.
Fed Chairman Jerome Powell said the economic outlook for the U.S. was favourable as the central bank announced its decision to hold rates steady, as expected, though forecast only moderate and slowing growth through 2020 and 2021.
New economic projections showed 13 of 17 Fed policymakers foresee no change in interest rates until at least 2021.
The kiwi dollar hit its highest since July after that, and was steady at $0.6581 on Thursday. The Aussie added 1% to hit a one-month high, and gave back only a fraction of that in early trade to hover around $0.6868.
Bond yields also slid after the decision.
Investor focus now shifts to the looming trade deadline, Christine Lagarde's first meeting at the helm of the ECB, and voting in the British election.
U.S. President Donald Trump is expected to meet with top advisers on Thursday about the tariff deadline, three people familiar with his plans told Reuters. A fourth person familiar with the administration's thinking said they expected the tariffs to be enforced.
Lagarde is all but certain to keep money taps wide open, but investors will be curious to tune in to her first post-meeting press conference to seek clues about a broader policy revamp that could become the cornerstone of her tenure.
That is due to begin at 1330 GMT. Before then, at 0700 GMT, voting begins in the United Kingdom, where polls have tightened recently but still predict a Conservative victory.
The pound is priced for a Conservative majority that could control parliament and lead Britain out of the European Union at the end of January, and anything short of that could prompt a slide. The dollar's weakness helped Sterling drift higher to $1.3210 on Thursday.
Voting ends at 2200 GMT, with exit polls and early results likely to flow after that and traders expecting an outcome as early as 0300 GMT on Friday.
"Prices should jump around...with likely sharp reactions as each constituency release their results," said Chris Weston, head of research at Melbourne brokerage Pepperstone.
"We are watching overnight implied volatility as it rolls over, and there is no doubt it will be sky-high, with traders pricing some punchy moves in the pound. One for the bravest of souls."
(Reporting by Tom Westbrook; Editing by Sam Holmes) ((firstname.lastname@example.org; +65 6318 4876;))