Fair Value Measurements (Total Gains and Losses Included in Earnings for Assets and Liabilites Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs) (Level 3) (Detail) - Fair Value, Inputs, Level 3 - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	$ 1	$ (13)
Mortgage Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	39	0
Corporate Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	1	0
Other Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	$ (39)	$ (13)