Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
AFS, Amortized Cost
Due in one year or less	$ 4,383
Due after one year through five years	8,102
Due after five years through ten years	881
Due after ten years	58,286
Debt Securities, Available-for-sale, Amortized Cost, Total	71,652	$ 73,833
AFS, Fair Value
Due in one year or less	4,404
Due after one year through five years	8,191
Due after five years through ten years	877
Due after ten years	52,918
Debt Securities, Available-for-sale, Total	66,390	67,464
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	48,973	50,640
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Fair Value
Debt Securities, Held-to-Maturity, Fair Value	39,611	40,286
U.S. Treasury
AFS, Amortized Cost
Due in one year or less	4,362
Due after one year through five years	7,859
Due after five years through ten years	430
Due after ten years	738
Debt Securities, Available-for-sale, Amortized Cost, Total	13,389	14,279
AFS, Fair Value
Due in one year or less	4,383
Due after one year through five years	7,944
Due after five years through ten years	428
Due after ten years	716
Debt Securities, Available-for-sale, Total	13,471	14,411
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	1
Due after ten years	458
Debt Securities, Available-for-sale, Amortized Cost, Total	459	441
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	1
Due after ten years	434
Debt Securities, Available-for-sale, Total	435	403
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	40
Due after ten years	54,132
Debt Securities, Available-for-sale, Amortized Cost, Total	54,173	55,769
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	40
Due after ten years	49,414
Debt Securities, Available-for-sale, Total	49,455	49,959
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	48,973
Debt Securities, Held-to-Maturity, Amortized Cost, Total	48,973	50,640
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	39,611
Debt Securities, Held-to-Maturity, Fair Value	39,611	40,286
Agency MBS – commercial
AFS, Amortized Cost
Due in one year or less	0
Due after one year through five years	169
Due after five years through ten years	255
Due after ten years	2,823
Debt Securities, Available-for-sale, Amortized Cost, Total	3,247	2,938
AFS, Fair Value
Due in one year or less	0
Due after one year through five years	171
Due after five years through ten years	254
Due after ten years	2,228
Debt Securities, Available-for-sale, Total	2,653	2,293
States and political subdivisions
AFS, Amortized Cost
Due in one year or less	21
Due after one year through five years	66
Due after five years through ten years	147
Due after ten years	135
Debt Securities, Available-for-sale, Amortized Cost, Total	369	390
AFS, Fair Value
Due in one year or less	21
Due after one year through five years	68
Due after five years through ten years	146
Due after ten years	126
Debt Securities, Available-for-sale, Total	361	382
Non-agency MBS
AFS, Amortized Cost
Due in one year or less	0
Other
AFS, Amortized Cost
Due after one year through five years	7
Due after five years through ten years	8
Due after ten years	0
Debt Securities, Available-for-sale, Amortized Cost, Total	15	16
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	8
Due after ten years	0
Debt Securities, Available-for-sale, Total	$ 15	$ 16