Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Interest income:
Interest-bearing deposits with banks	$ (4)	$ 4	$ (13)	$ 85
Investment securities:
Investment securities available-for-sale	145	189	285	404
Investment securities held-to-maturity	163	227	343	496
Investment securities purchased under money market liquidity facility	0	70	4	78
Total investment securities	308	486	632	978
Securities purchased under resale agreements	3	24	13	89
Loans	157	156	298	340
Other interest-earning assets	3	4	8	50
Total interest income	467	674	938	1,542
Interest expense:
Interest-bearing deposits	(65)	(54)	(134)	14
Short term borrowings under money market liquidity facility	0	58	4	64
Securities sold under repurchase agreements	0	1	0	3
Other short-term borrowings	1	5	1	15
Long-term debt	54	95	114	183
Other interest-bearing liabilities	10	10	19	40
Total interest expense	0	115	4	319
Net interest income	$ 467	$ 559	$ 934	$ 1,223