Goodwill and Other Intangible Assets - Narrative (Details) $ in Millions		12 Months Ended
	Jul. 01, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jul. 17, 2020 USD ($) branch	Dec. 31, 2017 USD ($)
Goodwill [Line Items]
Goodwill		$ 1,511	$ 1,433	$ 1,433		$ 1,387
Purchase accounting gain		533	0	0
Amortization expense		40	$ 25	$ 26
IBERIABANK (IBKC)
Goodwill [Line Items]
Goodwill	$ (533)
Purchase accounting gain	$ 533	533
Number of bank branches | branch					30
IBERIABANK (IBKC) | Core deposit intangibles
Goodwill [Line Items]
Finite-Lived Intangible Assets, Net		207
IBERIABANK (IBKC) | Customer-Related Intangible Assets
Goodwill [Line Items]
Finite-Lived Intangible Assets, Net		14
IBERIABANK (IBKC) | Purchased Credit Card Intangible Assets
Goodwill [Line Items]
Finite-Lived Intangible Assets, Net		10
IBERIABANK (IBKC) | State Banking Licenses
Goodwill [Line Items]
Finite-Lived Intangible Assets, Net		10
SunTrust Banks, Inc. Branches
Goodwill [Line Items]
Goodwill		78			$ 78
Number of bank branches | branch					30
SunTrust Banks, Inc. Branches | Core deposit intangibles
Goodwill [Line Items]
Finite-Lived Intangible Assets, Net		$ 7