Subsequent Event (Details)	Feb. 24, 2022 USD ($)	Jan. 03, 2022 USD ($) $ / shares shares	Oct. 15, 2020 USD ($) director $ / shares shares
BancShare Class A Common Stock
Subsequent Event [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 1.00
Number of shares issued (in shares) | shares			6,100,000
Number of fractional shares issued (in shares) | shares			8,800
payment for fractional shares			$ 7,200,000
Series B Preferred Stock
Subsequent Event [Line Items]
Common stock, conversion ratio			1
5.625% Non-Cumulative Perpetual Preferred Stock, Series C
Subsequent Event [Line Items]
Common stock, conversion ratio			1
CIT Group Inc.
Subsequent Event [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 0.01
CIT Group Inc. | BancShare Class A Common Stock
Subsequent Event [Line Items]
Common stock, conversion ratio			0.062
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) | $ / shares			$ 0.01
CIT Group Inc. | Non-Cumulative Perpetual Preferred Stock, Series B
Subsequent Event [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.01
Preferred Stock, dividend rate, percentage			5.625%
Subsequent Event
Subsequent Event [Line Items]
Preferred stock, non-callable period, extended term		5 years
Subsequent Event | Senior Notes
Subsequent Event [Line Items]
Extinguishment of debt, amount	$ 2,900,000,000
Subsequent Event | Senior Notes | 5.000% Senior Unsecured Notes Due Aug 2022
Subsequent Event [Line Items]
Extinguishment of debt, amount	1,100,000,000
Subsequent Event | Senior Notes | 5.000% Senior Unsecured Notes Due Aug 2023
Subsequent Event [Line Items]
Extinguishment of debt, amount	750,000,000
Subsequent Event | Senior Notes | 4.750% Senior Unsecured Notes Due Feb 2024
Subsequent Event [Line Items]
Extinguishment of debt, amount	500,000,000
Subsequent Event | Senior Notes | 5.250% Senior Unsecured Notes Due Mar 2025
Subsequent Event [Line Items]
Extinguishment of debt, amount	$ 500,000,000
Subsequent Event | Series B Preferred Stock
Subsequent Event [Line Items]
Preferred stock, shares outstanding | shares		325,000
Preferred stock, liquidation preference (in dollars per share) | $ / shares		$ 1,000
Preferred stock, liquidation preference		$ 325,000,000
Subsequent Event | 5.625% Non-Cumulative Perpetual Preferred Stock, Series C
Subsequent Event [Line Items]
Preferred stock, shares outstanding | shares		8,000,000
Preferred stock, liquidation preference (in dollars per share) | $ / shares		$ 25
Preferred stock, liquidation preference		$ 200,000,000
CIT Group Inc.
Subsequent Event [Line Items]
Number of directors of new entity | director			14
CIT Group Inc. | Subsequent Event | Senior Notes | 5.000% Senior Unsecured Notes Due Aug 2022
Subsequent Event [Line Items]
Liability assumed		$ 1,250,000,000
Debt interest rate		5.00%
CIT Group Inc. | Subsequent Event | Senior Notes | 5.000% Senior Unsecured Notes Due Aug 2023
Subsequent Event [Line Items]
Liability assumed		$ 750,000,000
Debt interest rate		5.00%
CIT Group Inc. | Subsequent Event | Senior Notes | 4.750% Senior Unsecured Notes Due Feb 2024
Subsequent Event [Line Items]
Liability assumed		$ 500,000,000
Debt interest rate		4.75%
CIT Group Inc. | Subsequent Event | Senior Notes | 5.250% Senior Unsecured Notes Due Mar 2025
Subsequent Event [Line Items]
Liability assumed		$ 500,000,000
Debt interest rate		5.25%
CIT Group Inc. | Subsequent Event | Senior Notes | 3.929% Senior Unsecured Fixed-to-Floating Rate Notes due 2024
Subsequent Event [Line Items]
Liability assumed		$ 500,000,000
Debt interest rate		3.929%
CIT Group Inc. | Subsequent Event | Senior Notes | 2.969% Senior Unsecured Fixed-to-Floating Rate Notes due 2025
Subsequent Event [Line Items]
Liability assumed		$ 550,000,000
Debt interest rate		2.969%
CIT Group Inc. | Subsequent Event | Senior Notes | 6.00% Senior Notes due 2036
Subsequent Event [Line Items]
Liability assumed		$ 500,000,000
Debt interest rate		6.00%
CIT Group Inc. | Subsequent Event | Subordinated Debt | 6.125% Subordinated Notes due 2028
Subsequent Event [Line Items]
Liability assumed		$ 400,000,000
Debt interest rate		6.125%
CIT Group Inc. | Subsequent Event | Subordinated Debt | 4.125% Fixed-to-Floating Rate Subordinated Notes due 2029
Subsequent Event [Line Items]
Liability assumed		$ 100,000,000
Debt interest rate		4.125%