Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
AFS, Amortized Cost
Due in one year or less	$ 2,597
Due after one year through five years	8,621
Due after five years through ten years	834
Due after ten years	70,946
Debt Securities, Available-for-sale, Amortized Cost, Total	82,998	$ 84,056
AFS, Fair Value
Due in one year or less	2,538
Due after one year through five years	8,038
Due after five years through ten years	805
Due after ten years	60,477
Debt Securities, Available-for-sale, Total	71,858	71,801
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	56,932	57,713
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Fair Value
Debt Securities, Held-to-Maturity, Fair Value	48,097	47,791
U.S. Treasury
AFS, Amortized Cost
Due in one year or less	2,587
Due after one year through five years	8,448
Due after five years through ten years	19
Due after ten years	29
Debt Securities, Available-for-sale, Amortized Cost, Total	11,083	11,080
AFS, Fair Value
Due in one year or less	2,528
Due after one year through five years	7,869
Due after five years through ten years	18
Due after ten years	26
Debt Securities, Available-for-sale, Total	10,441	10,295
GSE
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	7
Due after five years through ten years	11
Due after ten years	314
Debt Securities, Available-for-sale, Amortized Cost, Total	332	339
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	7
Due after five years through ten years	10
Due after ten years	284
Debt Securities, Available-for-sale, Total	301	303
Agency MBS - residential
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	65
Due after five years through ten years	580
Due after ten years	63,737
Debt Securities, Available-for-sale, Amortized Cost, Total	64,382	65,377
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	62
Due after five years through ten years	547
Due after ten years	54,566
Debt Securities, Available-for-sale, Total	55,175	55,225
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	56,932
Debt Securities, Held-to-Maturity, Amortized Cost, Total	56,932	57,713
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	48,097
Debt Securities, Held-to-Maturity, Fair Value	48,097	47,791
Agency MBS - commercial
AFS, Amortized Cost
Due in one year or less	1
Due after one year through five years	7
Due after five years through ten years	71
Due after ten years	2,793
Debt Securities, Available-for-sale, Amortized Cost, Total	2,872	2,887
AFS, Fair Value
Due in one year or less	1
Due after one year through five years	7
Due after five years through ten years	68
Due after ten years	2,322
Debt Securities, Available-for-sale, Total	2,398	2,424
States and political subdivisions
AFS, Amortized Cost
Due in one year or less	3
Due after one year through five years	94
Due after five years through ten years	139
Due after ten years	189
Debt Securities, Available-for-sale, Amortized Cost, Total	425	425
AFS, Fair Value
Due in one year or less	3
Due after one year through five years	93
Due after five years through ten years	148
Due after ten years	181
Debt Securities, Available-for-sale, Total	425	416
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	3,884
Debt Securities, Available-for-sale, Amortized Cost, Total	3,884	3,927
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	3,098
Debt Securities, Available-for-sale, Total	3,098	3,117
Other
AFS, Amortized Cost
Due in one year or less	6
Due after one year through five years	0
Due after five years through ten years	14
Due after ten years	0
Debt Securities, Available-for-sale, Amortized Cost, Total	20	21
AFS, Fair Value
Due in one year or less	6
Due after one year through five years	0
Due after five years through ten years	14
Due after ten years	0
Debt Securities, Available-for-sale, Total	$ 20	$ 21