Fair Value Measurements (Total Gains and Losses Included in Earning Attributable to Changes in Unrealized Gains and Losses Related to Level 3 Assets and Liabilites Still Held at Year End) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Change In Unrealized Gains Losses Included In Earnings	$ (20)	$ 78
Mortgage Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Change In Unrealized Gains Losses Included In Earnings	(7)	30
Other Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Change In Unrealized Gains Losses Included In Earnings	$ (13)	$ 48