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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	$ (53)	$ 28	$ (94)	$ 133
Mortgage Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	(6)	42	(27)	129
Corporate Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	0	0	2	1
Other Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gains and losses included in earnings	$ (47)	$ (14)	$ (69)	$ 3