Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	$ 286	$ 324
Liability derivatives, fair value	679	943
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	1	18
Liability derivatives, fair value	55	10
Fair value hedges:
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	232	256
Liability derivatives, fair value	584	898
Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	53	50
Liability derivatives, fair value	40	35
Interest rate swap agreements | Fair value hedges: | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	0	12
Liability derivatives, fair value	38	2
Commitments to sell real estate loans | Fair value hedges: | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	1	6
Liability derivatives, fair value	17	8
Commitments to sell real estate loans | Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	24	35
Liability derivatives, fair value	19	3
Mortgage-related commitments to originate real estate loans for sale | Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	29	15
Liability derivatives, fair value	21	32
Interest Rate Contracts | Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	218	237
Liability derivatives, fair value	571	879
Foreign exchange and other option and futures contracts | Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	14	19
Liability derivatives, fair value	$ 13	$ 19