Investment Securities - Gross Unrealized Losses and Fair Values of Investments in Continuous Unrealized Loss Positions (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
AFS securities, Fair Value
Less than 12 months	$ 286	$ 21,646
12 months or more	360	1,594
Total	646	23,240
AFS securities, Unrealized Losses
Less than 12 months	2	157
12 months or more	9	20
Total	11	177
U.S. Treasury
AFS securities, Fair Value
Less than 12 months	33	702
12 months or more	0	0
Total	33	702
AFS securities, Unrealized Losses
Less than 12 months	0	6
12 months or more	0	0
Total	0	6
US Government-sponsored Enterprises Debt Securities
AFS securities, Fair Value
Less than 12 months		6
12 months or more		0
Total		6
AFS securities, Unrealized Losses
Less than 12 months		0
12 months or more		0
Total		0
Agency MBS | Residential Mortgage Backed Securities
AFS securities, Fair Value
Less than 12 months	160	20,328
12 months or more	287	1,326
Total	447	21,654
AFS securities, Unrealized Losses
Less than 12 months	1	145
12 months or more	5	13
Total	6	158
Agency MBS | Commercial Mortgage Backed Securities
AFS securities, Fair Value
Less than 12 months	0	545
12 months or more	21	124
Total	21	669
AFS securities, Unrealized Losses
Less than 12 months	0	5
12 months or more	0	2
Total	0	7
States and political subdivisions
AFS securities, Fair Value
Less than 12 months	61	65
12 months or more	52	144
Total	113	209
AFS securities, Unrealized Losses
Less than 12 months	0	1
12 months or more	4	5
Total	4	$ 6
Other
AFS securities, Fair Value
Less than 12 months	32
12 months or more	0
Total	32
AFS securities, Unrealized Losses
Less than 12 months	1
12 months or more	0
Total	$ 1