Business Combination - Merger-Related Expenses (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020		Mar. 31, 2019
Business Acquisition [Line Items]
Compensation and benefits	$ 647		$ 610	[1]
Technology and communications	93		83	[1]
Net occupancy expense	82	[2]	75	[1]
Marketing expense	31		36	[1]
Other noninterest expense	249		213
Total noninterest expense	1,200		1,097	[1]
MB Financial, Inc.
Business Acquisition [Line Items]
Compensation and benefits	2		35
Technology and communications	3		11
Net occupancy expense	1
Marketing expense			4
Other noninterest expense	1		26
Total noninterest expense	$ 7		$ 76

[1] During the first quarter of 2020, certain noninterest income and noninterest expense line items were reclassified to better align disclosures to business activities. These reclassifications were retrospectively applied to all prior periods presented. Total noninterest income and noninterest expense did not change as a result of these reclassifications.

[2] Includes impairment losses and termination charges of $2 for ROU assets related to certain operating leases. For more information refer to Note 10.