Short-Term Borrowings - Summary of Short-Term Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Short-term borrowings	$ 2,124	$ 2,198
Trading Liabilities
Short-term Debt [Line Items]
Average balance	540	457	$ 503
Short-term borrowings	426	353	506
Maximum month-end outstanding	$ 685	$ 983	$ 754
Average rate for the year	1.11%	1.24%	2.48%
Average rate at year-end	1.62%	0.77%	2.07%
Federal Funds Purchased
Short-term Debt [Line Items]
Average balance	$ 949	$ 862	$ 738
Short-term borrowings	775	845	548
Maximum month-end outstanding	$ 1,037	$ 1,487	$ 1,282
Average rate for the year	0.12%	0.34%	2.08%
Average rate at year-end	0.10%	0.10%	1.55%
Securities Sold Under Agreements to Repurchase
Short-term Debt [Line Items]
Average balance	$ 1,235	$ 1,109	$ 701
Short-term borrowings	1,247	1,187	717
Maximum month-end outstanding	$ 1,615	$ 1,661	$ 772
Average rate for the year	0.30%	0.50%	2.07%
Average rate at year-end	0.11%	0.26%	1.72%
Other Short-term Borrowings
Short-term Debt [Line Items]
Average balance	$ 124	$ 626	$ 538
Short-term borrowings	102	166	2,253
Maximum month-end outstanding	$ 146	$ 4,061	$ 2,276
Average rate for the year	0.09%	0.84%	2.10%
Average rate at year-end	0.08%	0.09%	2.14%