Fair Value Measurement - Schedule of Assets Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 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	1,218	949
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	241,556	251,468
Loans held for sale	0	3
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	129	182
Loans held for sale	38	178
Other assets	100	35
Total assets	267	395
Equity investments accounted for under measurement alternative	24
Foreclosed property and repossessed assets, fair value disclosure	57	17
Long lived assets held for sale	19	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	38	177
Other assets	0	0
Total assets	38	177
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans held for investment	129	182
Loans held for sale	0	1
Other assets	100	35
Total assets	$ 229	$ 218