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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2024 | Mar. 31, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023 | Sep. 30, 2023 | Dec. 31, 2023 | Mar. 31, 2023 | Dec. 31, 2022
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Notional amounts of derivative contracts entered into for trading account purposes | $ 29,755 |  |  | $ 29,755 |  |  | $ 26,977 |  |
Shareholders' equity | 28,424 | $ 27,169 | $ 25,801 | 28,424 | $ 25,801 |  | 26,957 | $ 25,377 | $ 25,318
Aggregate fair value of derivative financial instruments in asset position | 208 |  |  | 208 |  |  | 179 |  |
Collateral relating to net asset positions | 205 |  |  | 205 |  |  | 179 |  |
Reduction in estimated fair value of interest rate contracts in asset position |  |  |  | (861) |  | $ (783) |  |  |
Reduction in estimated fair value of interest rate contracts in liability position |  |  |  | (16) |  | $ (32) |  |  |
Cash Flow Hedges |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Shareholders' equity | (246) |  |  | (246) |  |  | (151) |  |
Equity, Attributable to Parent, Before Tax | 330 |  | 436 | 330 | 436 |  | 203 |  | $ 336
Fair value hedges: |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Impact of estimated fair value gain (losses) on hedging instruments |  |  |  | 113 |  |  | 43 |  |
Cash flow hedges: |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Impact of estimated fair value gain (losses) on hedging instruments |  |  |  | 329 |  |  | 214 |  |
Clearinghouse Credit Facilities |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Amount of initial margin posted | 178 |  |  | 178 |  |  | 129 |  |
Interest Income |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Change in cash flow hedges derivative instruments, fair value net |  | $ (99) | (49) |  |  |  |  |  |
Changes in Cash Flow Hedges Derivative Instruments At Fair Value Net | (186) |  | (108) | (186) | (108) |  |  |  |
Interest rate swap agreements |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Increase decrease in net interest income due to interest rate swap agreements | $ (113) |  | $ (63) | $ (213) | $ (132) |  |  |  |
Derivative Instrument, Gain (Loss) Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration] | Interest and Dividend Income, Operating |  | Interest and Dividend Income, Operating | Interest and Dividend Income, Operating | Interest and Dividend Income, Operating |  |  |  |
Interest rate swap agreements | Maturity Period 2025 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Equity, Attributable to Parent, Before Tax | $ (189) |  |  | $ (189) |  |  |  |  |
Interest rate swap agreements | Maturity Period 2026 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Equity, Attributable to Parent, Before Tax | (148) |  |  | (148) |  |  |  |  |
Interest rate swap agreements | Maturity Period 2027 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Equity, Attributable to Parent, Before Tax | (7) |  |  | (7) |  |  |  |  |
Interest Rate Contracts | Not Designated as Hedging Instrument |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Notional amounts of derivative contracts entered into for trading account purposes | 43,200 |  |  | 43,200 |  |  | 44,400 |  |
Foreign exchange and other option and futures contracts | Not Designated as Hedging Instrument |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Notional amounts of derivative contracts entered into for trading account purposes | 1,500 |  |  | 1,500 |  |  |  |  |
Forward-Starting Interest Rate Swap Agreements | Fair value hedges: |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Notional amounts of derivative contracts entered into for trading account purposes | 1,900 |  |  | 1,900 |  |  | 1,000 |  |
Forward-Starting Interest Rate Swap Agreements | Cash flow hedges: |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Notional amounts of derivative contracts entered into for trading account purposes | $ 7,500 |  |  | $ 7,500 |  |  | $ 9,000 |  |

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