Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Interest income:
Interest-bearing deposits with banks	$ (6)	$ 98	$ 79	$ 326
Investment securities:
U.S. Treasury and federal agencies	254	363	922	1,092
State and political subdivisions	9	12	29	37
Other investments	77	126	289	374
Investment securities purchased under money market liquidity facility	25	0	103	0
Total investment securities	365	501	1,343	1,503
Securities purchased under resale agreements	20	101	109	289
Loans	138	194	479	587
Other interest-earning assets	3	107	52	330
Total interest income	520	1,001	2,062	3,035
Interest expense:
Interest-bearing deposits	(61)	173	(47)	553
Investment securities purchased under money market liquidity facility	23	0	87	0
Securities sold under repurchase agreements	0	7	3	27
Other short-term borrowings	2	8	17	18
Long-term debt	69	99	252	312
Other interest-bearing liabilities	9	70	49	195
Total interest expense	42	357	361	1,105
Net interest income	$ 478	$ 644	$ 1,701	$ 1,930