Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 255	$ 324
Liability Derivatives	822	943
Fair Value Hedges
Derivatives, Fair Value [Line Items]
Asset Derivatives	206	256
Liability Derivatives	787	898
Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset Derivatives	6	18
Liability Derivatives	3	10
Fair Value Hedges | Derivatives Not Designated and Qualifying as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	43	50
Liability Derivatives	32	35
Interest rate swap agreements | Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset Derivatives	2	12
Liability Derivatives	3	2
Commitments to sell real estate loans | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Liability Derivatives	0
Commitments to sell real estate loans | Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset Derivatives	4	6
Liability Derivatives		8
Commitments to sell real estate loans | Fair Value Hedges | Derivatives Not Designated and Qualifying as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	39	35
Liability Derivatives	0	3
Commitments to originate real estate loans for sale | Fair Value Hedges | Derivatives Not Designated and Qualifying as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	4	15
Liability Derivatives	32	32
Interest Rate Contracts | Fair Value Hedges | Derivatives Not Designated and Qualifying as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	185	237
Liability Derivatives	769	879
Foreign exchange and other option and futures contracts | Fair Value Hedges | Derivatives Not Designated and Qualifying as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	21	19
Liability Derivatives	$ 18	$ 19