Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
AFS, Amortized Cost
Due in one year or less	$ 748
Due after one year through five years	9,777
Due after five years through ten years	1,703
Due after ten years	142,860
Debt Securities, Available-for-sale, Amortized Cost, Total	155,088	$ 118,618
AFS, Fair Value
Due in one year or less	754
Due after one year through five years	9,714
Due after five years through ten years	1,734
Due after ten years	140,921
Debt Securities, Available-for-sale, Total	153,123	120,788
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	1,494
Debt Securities, Held-to-Maturity, Amortized Cost, Total	1,494	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Fair Value
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	1,495
Debt Securities, Held-to-Maturity, Fair Value	1,495	0
U.S. Treasury
AFS, Amortized Cost
Due in one year or less	290
Due after one year through five years	8,623
Due after five years through ten years	979
Due after ten years	0
Debt Securities, Available-for-sale, Amortized Cost, Total	9,892	1,721
AFS, Fair Value
Due in one year or less	290
Due after one year through five years	8,532
Due after five years through ten years	973
Due after ten years	0
Debt Securities, Available-for-sale, Total	9,795	1,746
GSE
AFS, Amortized Cost
Due in one year or less	426
Due after one year through five years	1,062
Due after five years through ten years	0
Due after ten years	179
Debt Securities, Available-for-sale, Amortized Cost, Total	1,667	1,840
AFS, Fair Value
Due in one year or less	432
Due after one year through five years	1,086
Due after five years through ten years	0
Due after ten years	180
Debt Securities, Available-for-sale, Total	1,698	1,917
Agency MBS | Agency MBS - residential
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	1
Due after five years through ten years	592
Due after ten years	135,293
Debt Securities, Available-for-sale, Amortized Cost, Total	135,886	111,589
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	1
Due after five years through ten years	611
Due after ten years	133,430
Debt Securities, Available-for-sale, Total	134,042	113,541
Agency MBS | Commercial Mortgage Backed Securities
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	8
Due after five years through ten years	15
Due after ten years	2,905
Debt Securities, Available-for-sale, Amortized Cost, Total	2,928	2,987
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	9
Due after five years through ten years	15
Due after ten years	2,858
Debt Securities, Available-for-sale, Total	2,882	3,057
States and political subdivisions
AFS, Amortized Cost
Due in one year or less	31
Due after one year through five years	77
Due after five years through ten years	117
Due after ten years	157
Debt Securities, Available-for-sale, Amortized Cost, Total	382	447
AFS, Fair Value
Due in one year or less	31
Due after one year through five years	80
Due after five years through ten years	135
Due after ten years	174
Debt Securities, Available-for-sale, Total	420	493
Non-agency MBS
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	4,305
Debt Securities, Available-for-sale, Amortized Cost, Total	4,305
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	4,258
Debt Securities, Available-for-sale, Total	4,258
Other
AFS, Amortized Cost
Due in one year or less	1
Due after one year through five years	6
Due after five years through ten years	0
Due after ten years	21
Debt Securities, Available-for-sale, Amortized Cost, Total	28	34
AFS, Fair Value
Due in one year or less	1
Due after one year through five years	6
Due after five years through ten years	0
Due after ten years	21
Debt Securities, Available-for-sale, Total	$ 28	$ 34