Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	$ 239	$ 255
Liability derivatives, fair value	632	822
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	13	6
Liability derivatives, fair value	1	3
Fair value hedges:
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	181	206
Liability derivatives, fair value	600	787
Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	45	43
Liability derivatives, fair value	31	32
Interest rate swap agreements | Fair value hedges: | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	12	2
Liability derivatives, fair value	0	3
Commitments to sell real estate loans | Fair value hedges: | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	1	4
Liability derivatives, fair value	1	0
Commitments to sell real estate loans | Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	28	39
Liability derivatives, fair value	6	0
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	17	4
Liability derivatives, fair value	25	32
Interest Rate Contracts | Fair value hedges: | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset derivatives, fair value	166	185
Liability derivatives, fair value	589	769
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	15	21
Liability derivatives, fair value	$ 11	$ 18