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Business Combinations - Merger (Details) | Oct. 15, 2020 $ / shares | Sep. 30, 2021 $ / shares | Dec. 31, 2020 $ / shares
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Subsequent Event [Line Items] |  |  |
Preferred stock, par value (in dollars per share) |  | $ 0.01 | $ 0.01
Class A Common Stock |  |  |
Subsequent Event [Line Items] |  |  |
Common stock, par value (in dollars per share) | $ 1.00 | $ 1 | $ 1
CIT Group Inc. |  |  |
Subsequent Event [Line Items] |  |  |
Common stock, par value (in dollars per share) | $ 0.01 |  |
CIT Group Inc. | BancShares Class A Common Stock |  |  |
Subsequent Event [Line Items] |  |  |
Conversion rate | 0.06200 |  |
CIT Group Inc. | Fixed-To-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series A |  |  |
Subsequent Event [Line Items] |  |  |
Preferred stock, par value (in dollars per share) | $ 0.01 |  |
CIT Group Inc. | Non-Cumulative Perpetual Preferred Stock, Series B |  |  |
Subsequent Event [Line Items] |  |  |
Preferred stock, par value (in dollars per share) | $ 0.01 |  |
Dividend rate (percentage) | 5.625% |  |
CIT Group Inc. | Series B Preferred Stock |  |  |
Subsequent Event [Line Items] |  |  |
Conversion rate | 1 |  |
CIT Group Inc. | Series C Preferred Stock |  |  |
Subsequent Event [Line Items] |  |  |
Conversion rate | 1 |  |

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