Fair Value Option Elected, Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Loans Receivable, Fair Value Disclosure	$ 206	$ 222
Trading Loans [Member]
Loans Receivable, Fair Value Disclosure	2,954	2,517
Aggregate Unpaid Principal Balance Under the Fair Value Option	(2,917)	(2,488)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	37	29
Loans Held For Sale [Member]
Loans Receivable, Fair Value Disclosure	2,252	3,540
Aggregate Unpaid Principal Balance Under the Fair Value Option	(2,180)	(3,516)
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	72	24
Loans Held For Investment [Member] | Performing Financial Instruments [Member]
Loans Receivable, Fair Value Disclosure	203	219
Aggregate Unpaid Principal Balance Under the Fair Value Option	(208)	(225)
Fair Value, Option, Loans Held as Assets, Aggregate Difference	(5)	(6)
Loans Held For Investment [Member] | Nonperforming Financing Receivable [Member]
Loans Receivable, Fair Value Disclosure	3	3
Aggregate Unpaid Principal Balance Under the Fair Value Option	(4)	(4)
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference	(1)	(1)
Brokered Time Deposits [Member]
Obligations, Fair Value Disclosure	207	78
Aggregate Unpaid Principal Balance Under the Fair Value Option	(208)	(80)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	(1)	(2)
Long-term Debt [Member]
Obligations, Fair Value Disclosure	758	963
Aggregate Unpaid Principal Balance Under the Fair Value Option	(736)	(924)
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	$ 22	$ 39