Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Interest income:
Interest-bearing deposits with banks	$ 0	$ (6)	$ (13)	$ 79
Investment securities:
Investment securities available-for-sale	150	169	435	609
Investment securities held-to-maturity	158	171	501	631
Investment securities purchased under money market liquidity facility	0	25	4	103
Total investment securities	308	365	940	1,343
Securities purchased under resale agreements	6	20	19	109
Loans	168	138	466	479
Other interest-earning assets	5	3	13	52
Total interest income	487	520	1,425	2,062
Interest expense:
Interest-bearing deposits	(62)	(61)	(196)	(47)
Short-term borrowings under money market liquidity facility	0	23	4	87
Securities sold under repurchase agreements	0	0	0	3
Other short-term borrowings	0	2	1	17
Long-term debt	51	69	165	252
Other interest-bearing liabilities	11	9	30	49
Total interest expense	0	42	4	361
Net interest income	$ 487	$ 478	$ 1,421	$ 1,701