Fair Values of Assets and Liabilities - Adjusted Carrying Values for Assets Measured at Fair Value on Nonrecurring Basis (Detail) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 173	$ 97
Other assets	24	21
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Other assets	0	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Other assets	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	173	97
Other assets	$ 24	$ 21