Business Combination - Additional Information (Details) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 22, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Total Assets	$ 168,802		$ 140,595	$ 168,802	$ 140,595		$ 146,069
Full-service Banking Centers	1,207			1,207
Total noninterest expense	$ 1,243		$ 1,001	$ 2,341	$ 2,011
MB Financial, Inc.
Business Acquisition [Line Items]
Total consideration paid		$ 3,608
Total Assets							$ 20,000
Full-service Banking Centers							86
Fair value of noncontrolling interest in acquiree						$ 197
Goodwill						1,809
Tax deductible goodwill						15
Total noninterest expense	109			185
Contractual balances on the purchased non credit impaired loans and leases						12,700
Fair value of the purchased non credit impaired loans and leases						$ 12,500
Cash consideration transferred per share | $ / shares						$ 5.54
Share consideration transferred | shares						1.45
Total value per share | $ / shares						$ 42.49
Closing price of common stock | $ / shares						$ 25.48
Concractual balances on PCI	992			992
Fair value for PCI	$ 737			$ 737
Locations							91