Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Interest income:
Interest-bearing deposits with banks	$ 4	$ 109	$ 85	$ 228
Investment securities:
U.S. Treasury and federal agencies	315	360	671	729
State and political subdivisions	9	13	20	25
Other investments	92	126	209	248
Investment securities purchased under money market liquidity facility	70	0	78	0
Total investment securities	486	499	978	1,002
Securities purchased under resale agreements	24	90	89	188
Loans	156	195	340	393
Other interest-earning assets	4	114	50	223
Total interest income	674	1,007	1,542	2,034
Interest expense:
Interest-bearing deposits	(54)	209	14	380
Investment securities purchased under money market liquidity facility	58	0	64	0
Securities sold under repurchase agreements	1	8	3	20
Other short-term borrowings	5	6	15	10
Long-term debt	95	107	183	213
Other interest-bearing liabilities	10	64	40	125
Total interest expense	115	394	319	748
Net interest income	$ 559	$ 613	$ 1,223	$ 1,286