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Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
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Schedule Of Available For Sale Securities And Held To Maturity [Line Items] |  |
Estimated fair value, Less than 12 months | $ 3,820 | $ 460
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses | 22 | 4
Estimated fair value, 12 months or more | 7,690 | 9,917
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses | 242 | 247
Held to maturity, Estimated fair value, Less than 12 months | 1,397 | 1,551
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses | 22 | 23
Held to maturity, Estimated fair value, 12 months or more | 12,410 | 11,844
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses | 1,200 | 1,012
Total investment securities, fair value less than 12 months | 5,217 | 2,011
Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses | 44 | 27
Total of investment securities, fair value, 12 Months or More | 20,100 | 21,761
Investment Securities Continuous Unrealized Loss Position Twelve Months or Longer Aggregate Losses | 1,442 | 1,259
U.S. Treasury and Federal Agencies [Member] |  |
Schedule Of Available For Sale Securities And Held To Maturity [Line Items] |  |
Estimated fair value, Less than 12 months | 2,242 | 229
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses | 10 | 1
Estimated fair value, 12 months or more | 5,177 | 7,474
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses | 89 | 112
Held to maturity, Estimated fair value, Less than 12 months | 49 | 50
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses | 1 |
Held to maturity, Estimated fair value, 12 months or more | 925 | 924
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses | 32 | 31
Commercial [Member] |  |
Schedule Of Available For Sale Securities And Held To Maturity [Line Items] |  |
Estimated fair value, Less than 12 months | 765 | 74
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses | 6 | 1
Estimated fair value, 12 months or more | 393 | 330
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses | 7 | 8
Held to maturity, Estimated fair value, Less than 12 months | 172 | 328
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses | 9 | 9
Held to maturity, Estimated fair value, 12 months or more | 1,709 | 1,575
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses | 145 | 121
Residential [Member] |  |
Schedule Of Available For Sale Securities And Held To Maturity [Line Items] |  |
Estimated fair value, Less than 12 months | 813 | 151
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses | 6 | 2
Estimated fair value, 12 months or more | 1,964 | 1,959
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses | 137 | 116
Held to maturity, Estimated fair value, Less than 12 months | 1,133 | 955
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses | 12 | 11
Held to maturity, Estimated fair value, 12 months or more | 7,459 | 7,139
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses | 923 | 791
Obligations of States and Political Subdivisions [Member] |  |
Schedule Of Available For Sale Securities And Held To Maturity [Line Items] |  |
Held to maturity, Estimated fair value, Less than 12 months | 43 | 218
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses |  | 3
Held to maturity, Estimated fair value, 12 months or more | 2,284 | 2,172
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses | 94 | 64
Other Debt Securities [Member] |  |
Schedule Of Available For Sale Securities And Held To Maturity [Line Items] |  |
Estimated fair value, Less than 12 months |  | 6
Estimated fair value, 12 months or more | 156 | 154
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses | 9 | 11
Privately Issued [Member] |  |
Schedule Of Available For Sale Securities And Held To Maturity [Line Items] |  |
Held to maturity, Estimated fair value, 12 months or more | 33 | 34
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses | $ 6 | $ 5

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