Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
IBERIABANK (IBKC)
Business Acquisition [Line Items]
Merger and integration expense	$ 95,968		$ 107,029
IBERIABANK (IBKC) | Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	29,984		34,394
IBERIABANK (IBKC) | Personal expense
Business Acquisition [Line Items]
Merger and integration expense	34,846		40,240
IBERIABANK (IBKC) | Contribution expense
Business Acquisition [Line Items]
Merger and integration expense	20,000		20,000
IBERIABANK (IBKC) | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	11,138		12,395
SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Merger and integration expense	4,825	$ 8,989	13,862	$ 23,296
SunTrust Banks, Inc. Branches | Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	1,196	3,507	3,322	9,852
SunTrust Banks, Inc. Branches | Personal expense
Business Acquisition [Line Items]
Merger and integration expense	303	1,473	786	4,462
SunTrust Banks, Inc. Branches | Contract employment and outsourcing
Business Acquisition [Line Items]
Merger and integration expense	203	223	929	240
SunTrust Banks, Inc. Branches | Net occupancy expense
Business Acquisition [Line Items]
Merger and integration expense	449	(76)	342	1,547
SunTrust Banks, Inc. Branches | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	951	1,022	2,276	2,170
SunTrust Banks, Inc. Branches | All other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 1,723	$ 2,840	$ 6,207	$ 5,025