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 (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value carrying amount, total loans	$ 2,263	$ 1,849
Contractual principal outstanding, total loans	2,266	1,848
Carrying amount over (under) contractual principal outstanding, total loans	(3)	1
Fair value carrying amount, time deposits	444	0
Contractual principal outstanding, time deposits	445	0
Carrying amount over (under) contractual principal outstanding, time deposits	$ (1)	$ 0