Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
AFS, Amortized Cost
Due in one year or less	$ 324
Due after one year through five years	8,693
Due after five years through ten years	1,752
Due after ten years	78,707
Debt Securities, Available-for-sale, Amortized Cost, Total	89,476	$ 155,088
AFS, Fair Value
Due in one year or less	322
Due after one year through five years	8,279
Due after five years through ten years	1,684
Due after ten years	74,468
Debt Securities, Available-for-sale, Total	84,753	153,123
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	61,662
Debt Securities, Held-to-Maturity, Amortized Cost, Total	61,662	1,494
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	59,124
Debt Securities, Held-to-Maturity, Fair Value	59,124	1,495
U.S. Treasury
AFS, Amortized Cost
Due in one year or less	309
Due after one year through five years	8,602
Due after five years through ten years	980
Due after ten years	0
Debt Securities, Available-for-sale, Amortized Cost, Total	9,891	9,892
AFS, Fair Value
Due in one year or less	307
Due after one year through five years	8,188
Due after five years through ten years	917
Due after ten years	0
Debt Securities, Available-for-sale, Total	9,412	9,795
GSE
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	257
Debt Securities, Available-for-sale, Amortized Cost, Total	257	1,667
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	245
Debt Securities, Available-for-sale, Total	245	1,698
Agency MBS
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date
Debt Securities, Held-to-Maturity, Amortized Cost, Total	61,662	1,494
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Fair Value
Debt Securities, Held-to-Maturity, Fair Value	59,124	1,495
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	633
Due after ten years	71,322
Debt Securities, Available-for-sale, Amortized Cost, Total	71,956	135,886
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	624
Due after ten years	67,613
Debt Securities, Available-for-sale, Total	68,238	134,042
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	2,808
Debt Securities, Available-for-sale, Amortized Cost, Total	2,831	2,928
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	8
Due after five years through ten years	14
Due after ten years	2,637
Debt Securities, Available-for-sale, Total	2,659	2,882
States and political subdivisions
AFS, Amortized Cost
Due in one year or less	15
Due after one year through five years	76
Due after five years through ten years	124
Due after ten years	151
Debt Securities, Available-for-sale, Amortized Cost, Total	366	382
AFS, Fair Value
Due in one year or less	15
Due after one year through five years	76
Due after five years through ten years	129
Due after ten years	150
Debt Securities, Available-for-sale, Total	370	420
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	4,149
Debt Securities, Available-for-sale, Amortized Cost, Total	4,149	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	3,803
Debt Securities, Available-for-sale, Total	3,803	4,258
Other
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	6
Due after five years through ten years	0
Due after ten years	20
Debt Securities, Available-for-sale, Amortized Cost, Total	26	28
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	6
Due after five years through ten years	0
Due after ten years	20
Debt Securities, Available-for-sale, Total	$ 26	$ 28