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