In a business combination in which the amount of net identifiable assets acquired and liabilities assumed exceeds the aggregate consideration transferred or to be transferred (as defined), this element represents the amount of gain recognized by the entity.

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Name:	us-gaap_BusinessCombinationBargainPurchaseGainRecognizedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Goodwill and Other Intangible Assets - Narrative (Details) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 01, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jul. 17, 2020 USD ($) branch	Dec. 31, 2019 USD ($)
Goodwill [Line Items]
Purchase accounting gain		$ 0	$ 532	$ (1)	$ 532
Goodwill		$ 1,511		$ 1,511		$ 1,511		$ 1,433
IBERIABANK (IBKC)
Goodwill [Line Items]
Purchase accounting gain	$ 531					531
Truist Bank Branches
Goodwill [Line Items]
Number of bank branches \| branch							30
Goodwill						$ 78	$ 78