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Acquisitions and Divestitures - Narrative (Details) $ in Millions |  | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jul. 01, 2020 USD ($) state numberNewPreferredStockSeries office shares | Mar. 31, 2021 USD ($) shares | Dec. 31, 2020 USD ($) shares | Jul. 17, 2020 branch | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |
Number of common stock issued | shares | 243,000,000 | 552,374,489 | 555,030,652 |  |  |
Number of new series of preferred stock | numberNewPreferredStockSeries | 3 |  |  |  |  |
Goodwill |  | $ 1,511.0 | $ 1,511.0 |  | $ 1,511.0 | $ 1,433.0
IBERIABANK (IBKC) |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Purchase accounting gain | $ 534.0 | 1.0 | 533.0 |  |  |
Goodwill | (534.0) |  |  |  |  |
Truist Bank Branches |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Goodwill |  | $ 78.0 | $ 78.0 |  |  |
Number of bank branches | branch |  |  |  | 30 |  |
IBERIABANK (IBKC) |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Equity interest issued, value assigned | $ 2,500.0 |  |  |  |  |
Number of offices | office | 319 |  |  |  |  |
Number of states | state | 12 |  |  |  |  |

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