Acquisitions and Divestitures - Merger and Integration Expenses (Details) - IBERIABANK (IBKC) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Merger and integration expense	$ 187	$ 155
Personnel expense
Business Acquisition [Line Items]
Merger and integration expense	56	66
Impairment of long-lived assets
Business Acquisition [Line Items]
Merger and integration expense	34	6
Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	21	39
Contract employment and outsourcing
Business Acquisition [Line Items]
Merger and integration expense	12	1
Advertising and public relations
Business Acquisition [Line Items]
Merger and integration expense	10	0
Contribution expense
Business Acquisition [Line Items]
Merger and integration expense	0	20
Other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 54	$ 23