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