Fair Value Measurement - Schedule of Assets Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	$ 0	$ 0
Loans held for sale	783	1,038
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	241,048	242,935
Loans held for sale	2	0
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	390	587
Loans held for sale	560	157
Other Assets, Fair Value Disclosure	35	83
Total	985	827
Nonrecurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed Properties and Repossessed Assets	34	43
Long Lived Assets Held for Sale	1	40
Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	0	0
Loans held for sale	559	157
Other Assets, Fair Value Disclosure	0	0
Total	559	157
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	390	587
Loans held for sale	1	0
Other Assets, Fair Value Disclosure	35	83
Total	$ 426	$ 670