Business Combination (Merger-Related Expenses) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Business Acquisition
Salaries, wages and incentives	$ 479	$ 447
Employee benefits	131	110
Technology and communications	83	68
Other noninterest expense	268	250
Total noninterest expense	1,097	$ 1,010
MB Financial, Inc.
Business Acquisition
Salaries, wages and incentives	32
Employee benefits	3
Technology and communications	11
Other noninterest expense	30
Total noninterest expense	$ 76