Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 318	$ 324
Liability Derivatives, Fair Value	1,072	943
Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	14	18
Liability Derivatives, Fair Value	2	10
Fair Value Hedges [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	258	256
Liability Derivatives, Fair Value	1,032	898
Fair Value Hedges [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	46	50
Liability Derivatives, Fair Value	38	35
Interest Rate Swap Agreements [Member] | Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	3	12
Liability Derivatives, Fair Value	1	2
Commitments to Sell Real Estate Loans [Member] | Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	11	6
Liability Derivatives, Fair Value	1	8
Commitments to Sell Real Estate Loans [Member] | Fair Value Hedges [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	40	35
Liability Derivatives, Fair Value	2	3
Commitments to Originate Real Estate Loans for Sale [Member] | Fair Value Hedges [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	6	15
Liability Derivatives, Fair Value	36	32
Interest Rate Contracts [Member] | Fair Value Hedges [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	243	237
Liability Derivatives, Fair Value	1,019	879
Foreign Exchange and Other Option and Futures Contracts [Member] | Fair Value Hedges [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	15	19
Liability Derivatives, Fair Value	$ 13	$ 19