Acquisitions and Divestitures - Narrative (Details) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 01, 2020 USD ($) office state newPreferredStockSeries shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) shares	Jul. 17, 2020 USD ($) branch	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Number of common stock issued (in shares) | shares	243,000,000	541,859,599		541,859,599		555,030,652
Number of new series of preferred stock | newPreferredStockSeries	3
Purchase accounting gain		$ 0	$ 532	$ (1)	$ 532
Goodwill		$ 1,511		$ 1,511		$ 1,511		$ 1,433
IBERIABANK (IBKC)
Business Acquisition [Line Items]
Equity interest issued, value assigned	$ 2,500
Purchase accounting gain	$ 531					531
Truist Bank Branches
Business Acquisition [Line Items]
Number of bank branches | branch							30
Goodwill						$ 78	$ 78
IBERIABANK (IBKC)
Business Acquisition [Line Items]
Number of offices | office	319
Number of states | state	12