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, 2020	Mar. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	$ (289)	$ (89)
Mortgage Banking Revenue
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	(267)	(58)
Other Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Gain and losses included in earnings	$ (22)	$ (31)