Assets and Liabilities Measured at Fair Value on a Recurring Basis (Additional Information) (Detail) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Trading, and Equity Securities, FV-NI	[1]	$ 6,259	$ 5,506
Fair Value, Inputs, Level 2 [Member]
Debt Securities, Trading, and Equity Securities, FV-NI		5,523	4,965
Total Return Swap [Member] | Trading Loans [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Trading, and Equity Securities, FV-NI		2,200	2,000
Commercial and Corporate Leveraged Loans [Member] | Trading Loans [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Trading, and Equity Securities, FV-NI		91	137
SBA Loans [Member] | Trading Loans [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Trading, and Equity Securities, FV-NI		$ 309	$ 366

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,382 million and $1,442 million at March 31, 2019 and December 31, 2018, respectively.