Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest income:
Interest-bearing deposits with banks	$ (9)	$ 81
Investment securities:
Investment securities available-for-sale	140	213
Investment securities held-to-maturity	180	271
Investment securities purchased under money market liquidity facility	4	8
Securities purchased under resale agreements	10	65
Loans	141	184
Other interest-earning assets	5	46
Total interest income	471	868
Interest expense:
Interest-bearing deposits	(69)	68
Short term borrowings under money market liquidity facility	4	6
Securities sold under repurchase agreements	0	2
Other short-term borrowings	0	10
Long-term debt	60	88
Other interest-bearing liabilities	9	30
Total interest expense	4	204
Net interest income	$ 467	$ 664