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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2024 | Jun. 30, 2024 | Mar. 31, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023 | Jun. 30, 2023 | Dec. 31, 2022
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Notional amounts of derivative contracts entered into for trading account purposes | $ 30,570 |  |  |  | $ 30,570 |  | $ 26,977 |  |
Shareholders' equity | 28,876 | $ 28,424 |  | $ 26,196 | 28,876 | $ 26,196 | 26,957 | $ 25,801 | $ 25,318
Aggregate fair value of derivative financial instruments in asset position | 94 |  |  |  | 94 |  | 179 |  |
Collateral relating to net asset positions | 87 |  |  |  | 87 |  | 179 |  |
Reduction in estimated fair value of interest rate contracts in asset position |  |  |  |  | (496) |  | (783) |  |
Reduction in estimated fair value of interest rate contracts in liability position |  |  |  |  | (51) |  | (32) |  |
Cash Flow Hedges |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Shareholders' equity | 45 |  |  |  | 45 |  | (151) |  |
Equity, Attributable to Parent, Before Tax | 59 |  |  | (529) | 59 | (529) | (203) |  | $ (336)
Fair value hedges: |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Impact of estimated fair value gain (losses) on hedging instruments |  |  | $ 43 |  | 15 |  |  |  |
Cash flow hedges: |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Impact of estimated fair value gain (losses) on hedging instruments |  |  | $ 214 |  | 89 |  |  |  |
Clearinghouse Credit Facilities |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Amount of initial margin posted | 154 |  |  |  | 154 |  | 129 |  |
Interest Income |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Change in cash flow hedges derivative instruments, fair value net |  | $ (102) |  | (65) |  |  |  |  |
Changes in Cash Flow Hedges Derivative Instruments At Fair Value Net | (288) |  |  | (173) | (288) | (173) |  |  |
Interest rate swap agreements |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Cash flow hedge reclassification before tax | $ (115) |  |  | $ (79) | $ (328) | $ (211) |  |  |
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 | $ (78) |  |  |  | $ (78) |  |  |  |
Interest rate swap agreements | Maturity Period 2026 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Equity, Attributable to Parent, Before Tax | 48 |  |  |  | 48 |  |  |  |
Interest rate swap agreements | Maturity Period 2027 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Equity, Attributable to Parent, Before Tax | 90 |  |  |  | 90 |  |  |  |
Interest rate swap agreements | Maturity Period 2028 |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Equity, Attributable to Parent, Before Tax | 1 |  |  |  | 1 |  |  |  |
Interest Rate Contracts | Not Designated as Hedging Instrument |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Notional amounts of derivative contracts entered into for trading account purposes | 42,500 |  |  |  | 42,500 |  | 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 | 1,400 |  |  |  | 1,400 |  | 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 | $ 6,600 |  |  |  | $ 6,600 |  | $ 9,000 |  |

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