Fair Value Option Elected, Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Trading, and Equity Securities, FV-NI	[1]	$ 5,676	$ 5,093
Loans Receivable, Fair Value Disclosure		168	196
Loans Held-for-sale, Fair Value Disclosure		1,822	1,577
Trading Loans [Member]
Debt Securities, Trading, and Equity Securities, FV-NI		2,171	2,149
Aggregate Unpaid Principal Balance Under the Fair Value Option		(2,160)	(2,111)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables		11	38
Loans Held-For-Sale [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Aggregate Unpaid Principal Balance Under the Fair Value Option			(1)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables			0
Loans Held-for-sale, Fair Value Disclosure			1
Loans Held-For-Sale [Member] | Performing Financial Instruments [Member]
Aggregate Unpaid Principal Balance Under the Fair Value Option		(1,775)	(1,533)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables		47	43
Loans Held-for-sale, Fair Value Disclosure		1,822	1,576
Loans Held-For-Investment [Member] | Performing Financial Instruments [Member]
Loans Receivable, Fair Value Disclosure		162	192
Aggregate Unpaid Principal Balance Under the Fair Value Option		(171)	(198)
Fair Value, Option, Loans Held as Assets, Aggregate Difference		(9)	(6)
Loans Held-For-Investment [Member] | Nonperforming Financing Receivable [Member]
Loans Receivable, Fair Value Disclosure		6	4
Aggregate Unpaid Principal Balance Under the Fair Value Option		(8)	(6)
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference		(2)	(2)
Brokered Time Deposits [Member]
Obligations, Fair Value Disclosure		384	236
Aggregate Unpaid Principal Balance Under the Fair Value Option		(379)	(233)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments		5	3
Long-term Debt [Member]
Obligations, Fair Value Disclosure		235	530
Aggregate Unpaid Principal Balance Under the Fair Value Option		(230)	(517)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments		$ 5	$ 13

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,362 million and $1,086 million at September 30, 2018 and December 31, 2017, respectively.