Investment Securities - Fair Value and Gross Unrealized Losses on Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value
Less than 12 months	$ 1,099	$ 4,128
12 months or more	444	383
Total	1,543	4,511
Unrealized Losses
Less than 12 months	(27)	(34)
12 months or more	(15)	(9)
Total	(42)	(43)
Agency mortgage-backed securities | Residential mortgage backed securities
Fair Value
Less than 12 months	0	2,159
12 months or more	1	4
Total	1	2,163
Unrealized Losses
Less than 12 months	0	(19)
12 months or more	0	0
Total	0	(19)
Agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months		1,602
12 months or more		0
Total		1,602
Unrealized Losses
Less than 12 months		(12)
12 months or more		0
Total		(12)
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	12
12 months or more	0
Total	12
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	1,087	367
12 months or more	443	379
Total	1,530	746
Unrealized Losses
Less than 12 months	(27)	(3)
12 months or more	(15)	(9)
Total	$ (42)	$ (12)