Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investment securities:
Interest-bearing deposits with banks	$ 81	$ 119
U.S. Treasury and federal agencies	356	369
State and political subdivisions	11	12
Other investments	117	122
Investment securities purchased under money market liquidity facility	8	0
Securities purchased under resale agreements	65	98
Loans	184	198
Other interest-earning assets	46	109
Total interest income	868	1,027
Interest expense:
Interest-bearing deposits	68	171
Investment securities purchased under money market liquidity facility	6	0
Securities sold under repurchase agreements	2	12
Other short-term borrowings	10	4
Long-term debt	88	106
Other interest-bearing liabilities	30	61
Total interest expense	204	354
Net interest income	$ 664	$ 673