Fair Value Measurement - Schedule of Assets Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
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	1,417	949
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	232,276	251,468
Loans held for sale	78	3
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	82	182
Loans held for sale	348	178
Other assets, fair value	99	35
Total	529	395
Nonrecurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments accounted for under measurement alternative	17
Foreclosed property and repossessed assets	75	17
Long lived assets held for sale	7	18
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	348	177
Other assets, fair value	0	0
Total	348	177
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	82	182
Loans held for sale	0	1
Other assets, fair value	99	35
Total	$ 181	$ 218