Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
AFS, Amortized Cost
Due in one year or less	$ 2,894
Due after one year through five years	7,700
Due after five years through ten years	762
Due after ten years	69,486
Debt Securities, Available-for-sale, Amortized Cost, Total	80,842	$ 84,056
AFS, Fair Value
Due in one year or less	2,813
Due after one year through five years	7,074
Due after five years through ten years	724
Due after ten years	58,354
Debt Securities, Available-for-sale, Total	68,965	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	55,958	57,713
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Fair Value
Debt Securities, Held-to-Maturity, Fair Value	45,956	47,791
U.S. Treasury
AFS, Amortized Cost
Due in one year or less	2,885
Due after one year through five years	7,492
Due after five years through ten years	17
Due after ten years	29
Debt Securities, Available-for-sale, Amortized Cost, Total	10,423	11,080
AFS, Fair Value
Due in one year or less	2,803
Due after one year through five years	6,874
Due after five years through ten years	15
Due after ten years	26
Debt Securities, Available-for-sale, Total	9,718	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	307
Debt Securities, Available-for-sale, Amortized Cost, Total	325	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	271
Debt Securities, Available-for-sale, Total	288	303
Agency MBS - residential
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	99
Due after five years through ten years	511
Due after ten years	62,373
Debt Securities, Available-for-sale, Amortized Cost, Total	62,983	65,377
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	93
Due after five years through ten years	476
Due after ten years	52,626
Debt Securities, Available-for-sale, Total	53,195	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	55,958
Debt Securities, Held-to-Maturity, Amortized Cost, Total	55,958	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	45,956
Debt Securities, Held-to-Maturity, Fair Value	45,956	47,791
Agency MBS - commercial
AFS, Amortized Cost
Due in one year or less	1
Due after one year through five years	0
Due after five years through ten years	71
Due after ten years	2,771
Debt Securities, Available-for-sale, Amortized Cost, Total	2,843	2,887
AFS, Fair Value
Due in one year or less	1
Due after one year through five years	0
Due after five years through ten years	66
Due after ten years	2,225
Debt Securities, Available-for-sale, Total	2,292	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	4
Due after one year through five years	92
Due after five years through ten years	144
Due after ten years	178
Debt Securities, Available-for-sale, Total	418	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	3,817
Debt Securities, Available-for-sale, Amortized Cost, Total	3,817	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	3,028
Debt Securities, Available-for-sale, Total	3,028	3,117
Other
AFS, Amortized Cost
Due in one year or less	5
Due after one year through five years	8
Due after five years through ten years	13
Due after ten years	0
Debt Securities, Available-for-sale, Amortized Cost, Total	26	21
AFS, Fair Value
Due in one year or less	5
Due after one year through five years	8
Due after five years through ten years	13
Due after ten years	0
Debt Securities, Available-for-sale, Total	$ 26	$ 21