Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investment securities:
Interest-bearing deposits with banks	$ 76	$ 416	$ 387
U.S. Treasury and federal agencies	1,174	1,443	1,178
State and political subdivisions	37	49	143
Other investments	366	505	560
Investment securities purchased under money market liquidity facility	117	0	0
Total Investment securities	1,694	1,997	1,881
Securities purchased under resale agreements	126	364	335
Loans and leases	624	769	687
Other interest-earning assets	55	395	372
Total interest income	2,575	3,941	3,662
Interest expense:
Interest-bearing deposits	(117)	663	363
Short term borrowings under money market liquidity facility	101	0	0
Securities sold under repurchase agreements	4	31	13
Other short-term borrowings	17	21	17
Long-term debt	312	414	389
Other interest-bearing liabilities	58	246	209
Total interest expense	375	1,375	991
Net interest income	$ 2,200	$ 2,566	$ 2,671