Short-Term Borrowings - Summary of Short-Term Borrowings and Weighted-Average Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Federal funds purchased	$ 281	$ 300
Other short-term borrowings	980	1,192
Federal Funds Purchased
Short-term Debt [Line Items]
Short-term borrowings, average	333	385
Short-term borrowings, maximum month-end balance	$ 365	$ 1,625
Short-term borrowngs, rate	0.13%	0.14%
Short-term borrowings, average rate	0.12%	0.58%
Other Short Term Borrowings
Short-term Debt [Line Items]
Short-term borrowings, average	$ 1,107	$ 1,709
Short-term borrowings, maximum month-end balance	$ 1,353	$ 4,542
Short-term borrowngs, rate	0.04%	0.19%
Short-term borrowings, average rate	0.15%	0.81%