Investment Securities - Fair Value and Gross Unrealized Losses on Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value
Less than 12 months	$ 2,769	$ 1,336
12 months or more	844	604
Total	3,613	1,940
Unrealized Losses
Less than 12 months	(63)	(20)
12 months or more	(20)	(17)
Total	(83)	(37)
Agency mortgage-backed securities | Residential mortgage backed securities
Fair Value
Less than 12 months	701	426
12 months or more	1	1
Total	702	427
Unrealized Losses
Less than 12 months	(20)	(8)
12 months or more	0	0
Total	(20)	(8)
Agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	1,632	388
12 months or more	0	0
Total	1,632	388
Unrealized Losses
Less than 12 months	(36)	(5)
12 months or more	0	0
Total	(36)	(5)
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	1	2
12 months or more	0	0
Total	1	2
Unrealized Losses
Less than 12 months	0	0
12 months or more	0	0
Total	0	0
Asset-backed securities and other debt securities
Fair Value
Less than 12 months	435	520
12 months or more	843	603
Total	1,278	1,123
Unrealized Losses
Less than 12 months	(7)	(7)
12 months or more	(20)	(17)
Total	$ (27)	$ (24)