Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
IBERIABANK (IBKC)
Business Acquisition [Line Items]
Merger and integration expense	$ 140	$ 11
IBERIABANK (IBKC) | Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	41	8
IBERIABANK (IBKC) | Personnel expense
Business Acquisition [Line Items]
Merger and integration expense	61	3
IBERIABANK (IBKC) | Contribution expense
Business Acquisition [Line Items]
Merger and integration expense	20	0
IBERIABANK (IBKC) | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	18	0
SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Merger and integration expense	20	22
SunTrust Banks, Inc. Branches | Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	2	11
SunTrust Banks, Inc. Branches | Personnel expense
Business Acquisition [Line Items]
Merger and integration expense	6	1
SunTrust Banks, Inc. Branches | Contract employment and outsourcing
Business Acquisition [Line Items]
Merger and integration expense	1	0
SunTrust Banks, Inc. Branches | Net occupancy expense
Business Acquisition [Line Items]
Merger and integration expense	1	1
SunTrust Banks, Inc. Branches | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	4	2
SunTrust Banks, Inc. Branches | All other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 6	$ 7