Fair Value Option Elected, Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Trading Loans [Member]
Obligations, Fair Value Disclosure	$ 2,680	$ 2,655
Aggregate Unpaid Principal Balance Under the Fair Value Option	(2,630)	(2,605)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	50	50
Loans Held For Sale [Member]
Obligations, Fair Value Disclosure	2,176	1,494
Aggregate Unpaid Principal Balance Under the Fair Value Option	(2,079)	(1,453)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	97	41
Loans Held For Investment [Member]
Fair Value, Option, Loans Held as Assets, Aggregate Difference	1	(5)
Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due, Aggregate Difference	0
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference	(2)	(2)
Loans Held For Investment [Member] | Performing Financial Instruments [Member]
Obligations, Fair Value Disclosure	240	254
Aggregate Unpaid Principal Balance Under the Fair Value Option	(239)	(259)
Loans Held For Investment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Obligations, Fair Value Disclosure	1
Aggregate Unpaid Principal Balance Under the Fair Value Option	(1)
Loans Held For Investment [Member] | Nonperforming Financing Receivable [Member]
Obligations, Fair Value Disclosure	5	3
Aggregate Unpaid Principal Balance Under the Fair Value Option	(7)	(5)
Brokered Time Deposits [Member]
Obligations, Fair Value Disclosure	49
Aggregate Unpaid Principal Balance Under the Fair Value Option	(50)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	(1)
Long-term Debt [Member]
Obligations, Fair Value Disclosure	970	973
Aggregate Unpaid Principal Balance Under the Fair Value Option	(907)	(907)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	$ 63	$ 66