Derivatives and Hedging Activities - Carrying Amount of Hedged Items Currently Designated in a Hedging Relationship and Related Cumulative Hedging Adjustment (Detail) - Derivative Contracts Accounted for as Hedges [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deposits at Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	$ 19,634	$ 11,924
Cumulative Hedging Adjustment	200	(156)
Unsecured short-term borrowings [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	6,008	4,450
Cumulative Hedging Adjustment	28	(12)
Unsecured long-term borrowings [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	87,874	68,839
Cumulative Hedging Adjustment	$ 7,292	$ 2,759