Fair Value Measurements - Quantitative Information about Nonrecurring Fair Value Measurement of Assets and Liabilities Classified as Level 3 (Detail) - Fair Value, Nonrecurring $ in Millions	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total assets at fair value on a non-recurring basis	$ 530	$ 480
Commercial loans held for sale
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total assets at fair value on a non-recurring basis	0	0
Commercial Loans
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total assets at fair value on a non-recurring basis	428	374
Level 3
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total assets at fair value on a non-recurring basis	428	374
Level 3 | Commercial loans held for sale
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total assets at fair value on a non-recurring basis	0	0
Level 3 | Commercial Loans
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total assets at fair value on a non-recurring basis	$ 428	$ 374
Loss severity rates | Level 3 | Commercial Loans | Minimum | Valuation of third-party appraisal on underlying collateral
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Range of Inputs	0	0.01
Loss severity rates | Level 3 | Commercial Loans | Maximum | Valuation of third-party appraisal on underlying collateral
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Range of Inputs	1	0.93
Loss severity rates | Level 3 | Commercial Loans | Weighted Average | Valuation of third-party appraisal on underlying collateral
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Range of Inputs	0.22	0.25