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	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	$ (338)	$ (57)	$ (191)
Mortgage Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	(233)	0	(113)
Corporate Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	2	2	2
Other Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	$ (107)	$ (59)	$ (80)