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Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023
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Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
AFS, less than 12 months, fair value | $ 747 | $ 460
AFS, less than 12 months, gross unrealized losses | 2 | 4
AFS, 12 months or longer, fair value | 5,021 | 9,917
AFS, 12 months or longer, gross unrealized losses | 106 | 247
Total investment securities, less than 12 months, fair value | 773 | 2,011
Total investment securities, less than 12 months, gross unrealized losses | 2 | 27
Total investment securities, 12 months or longer, fair value | 17,468 | 21,761
Total investment securities, 12 months or longer, gross unrealized losses | 921 | 1,259
Schedule of Held-to-Maturity Securities [Line Items] |  |
HTM, less than 12 months, fair value | 26 | 1,551
HTM, Less than 12 months, gross unrealized losses | 0 | 23
HTM, 12 months or longer, fair value | 12,447 | 11,844
HTM, 12 months or longer, gross unrealized losses | 815 | 1,012
U.S. Treasury and federal agencies |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
AFS, less than 12 months, fair value | 125 | 229
AFS, less than 12 months, gross unrealized losses | 0 | 1
AFS, 12 months or longer, fair value | 3,069 | 7,474
AFS, 12 months or longer, gross unrealized losses | 26 | 112
Schedule of Held-to-Maturity Securities [Line Items] |  |
HTM, less than 12 months, fair value | 0 | 50
HTM, Less than 12 months, gross unrealized losses | 0 | 0
HTM, 12 months or longer, fair value | 949 | 924
HTM, 12 months or longer, gross unrealized losses | 14 | 31
Commercial |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
AFS, less than 12 months, fair value | 395 | 74
AFS, less than 12 months, gross unrealized losses | 2 | 1
AFS, 12 months or longer, fair value | 128 | 330
AFS, 12 months or longer, gross unrealized losses | 1 | 8
Schedule of Held-to-Maturity Securities [Line Items] |  |
HTM, less than 12 months, fair value | 0 | 328
HTM, Less than 12 months, gross unrealized losses | 0 | 9
HTM, 12 months or longer, fair value | 1,957 | 1,575
HTM, 12 months or longer, gross unrealized losses | 81 | 121
Residential |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
AFS, less than 12 months, fair value | 227 | 151
AFS, less than 12 months, gross unrealized losses | 0 | 2
AFS, 12 months or longer, fair value | 1,760 | 1,959
AFS, 12 months or longer, gross unrealized losses | 77 | 116
Schedule of Held-to-Maturity Securities [Line Items] |  |
HTM, less than 12 months, fair value | 0 | 955
HTM, Less than 12 months, gross unrealized losses | 0 | 11
HTM, 12 months or longer, fair value | 7,318 | 7,139
HTM, 12 months or longer, gross unrealized losses | 646 | 791
Other debt securities |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
AFS, less than 12 months, fair value | 0 | 6
AFS, less than 12 months, gross unrealized losses | 0 | 0
AFS, 12 months or longer, fair value | 64 | 154
AFS, 12 months or longer, gross unrealized losses | 2 | 11
Obligations of states and political subdivisions |  |
Schedule of Held-to-Maturity Securities [Line Items] |  |
HTM, less than 12 months, fair value | 26 | 218
HTM, Less than 12 months, gross unrealized losses | 0 | 3
HTM, 12 months or longer, fair value | 2,192 | 2,172
HTM, 12 months or longer, gross unrealized losses | 71 | 64
Privately issued |  |
Schedule of Held-to-Maturity Securities [Line Items] |  |
HTM, less than 12 months, fair value | 0 | 0
HTM, Less than 12 months, gross unrealized losses | 0 | 0
HTM, 12 months or longer, fair value | 31 | 34
HTM, 12 months or longer, gross unrealized losses | $ 3 | $ 5

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