Investment Securities - Fair Value and Gross Unrealized Losses on Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value
Less than 12 months	$ 1,336	$ 4,128
12 months or more	604	383
Total	1,940	4,511
Unrealized Losses
Less than 12 months	(20)	(34)
12 months or more	(17)	(9)
Total	(37)	(43)
Agency mortgage-backed securities | Residential mortgage backed securities
Fair Value
Less than 12 months	426	2,159
12 months or more	1	4
Total	427	2,163
Unrealized Losses
Less than 12 months	(8)	(19)
12 months or more	0	0
Total	(8)	(19)
Agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	388	1,602
12 months or more	0	0
Total	388	1,602
Unrealized Losses
Less than 12 months	(5)	(12)
12 months or more	0	0
Total	(5)	(12)
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	2
12 months or more	0
Total	2
Unrealized Losses
Less than 12 months	0
12 months or more	0
Total	0
Asset-backed securities and other debt securities
Fair Value
Less than 12 months	520	367
12 months or more	603	379
Total	1,123	746
Unrealized Losses
Less than 12 months	(7)	(3)
12 months or more	(17)	(9)
Total	$ (24)	$ (12)