Fair Values of Assets and Liabilities - Differences Between Aggregate Fair Value Carrying Amount of MLHFS for which Fair Value Option has been Elected and Aggregate Unpaid Principal Amount Contractually Obligated to Receive at Maturity (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair value option loan held as assets aggregate amount in non accrual status	$ 1	$ 1
Contractual principal amount outstanding of loans in non accrual status measured using fair value option	1	1
Fair value option loans held ase assets ninety days or more past due	3	1
Contractual principal amount outstanding of loans ninety days or more past due	$ 3	$ 1