Borrowings (Schedule of Long-Term Borrowings) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term borrowings	$ 8,531.2	$ 14,935.5
CIT Group Inc.
Debt Instrument [Line Items]
Long-term borrowings	3,748.0
Subsidiaries
Debt Instrument [Line Items]
Long-term borrowings	4,783.2
Senior Unsecured
Debt Instrument [Line Items]
Long-term borrowings	3,748.0	10,599.0
Senior Unsecured | CIT Group Inc.
Debt Instrument [Line Items]
Long-term borrowings	3,748.0
Senior Unsecured | Subsidiaries
Debt Instrument [Line Items]
Long-term borrowings	0.0
Secured Borrowings
Debt Instrument [Line Items]
Long-term borrowings	1,637.7	1,925.7
Secured Borrowings | CIT Group Inc.
Debt Instrument [Line Items]
Long-term borrowings	0.0
Secured Borrowings | Subsidiaries
Debt Instrument [Line Items]
Long-term borrowings	1,637.7
FHLB advances
Debt Instrument [Line Items]
Long-term borrowings	3,145.5	$ 2,410.8
FHLB advances | CIT Group Inc.
Debt Instrument [Line Items]
Long-term borrowings	0.0
FHLB advances | Subsidiaries
Debt Instrument [Line Items]
Long-term borrowings	$ 3,145.5