Fair Value (Carrying And Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financial Assets
Cash and interest bearing deposits	[1]	$ 1,440.1	$ 5,608.5
Financial Liabilities
Credit balances of factoring clients		(1,468.6)	(1,292.0)	$ (1,344.0)
Debt Securities AFS		6,123.6
Securities carried at fair value with changes recorded in net income		0.4	283.5
Carrying Value
Financial Assets
Cash and interest bearing deposits		1,718.7	6,430.6
Assets held for sale (excluding leases)		1,011.4	428.4
Loans (excluding leases)		26,428.1	26,683.0
Securities purchased under agreement to resell		150.0
Investment securities		6,469.9	4,491.1
Indemnification assets		113.5	233.4
Other assets subject to fair value disclosure and unsecured counterparty receivables		542.2	712.2
Financial Liabilities
Deposits		(29,586.5)	(32,323.2)
Borrowings		(9,043.8)	(15,097.8)
Credit balances of factoring clients		(1,468.6)	(1,292.0)
Other liabilities subject to fair value disclosure		(725.2)	(1,003.6)
Carrying Value | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		68.5	94.7
Financial Liabilities
Derivative liabilities at fair value		(68.3)	(68.8)
Carrying Value | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.2	16.9
Financial Liabilities
Derivative liabilities at fair value		(18.7)
Estimated Fair Value
Financial Assets
Cash and interest bearing deposits		1,718.7	6,430.6
Assets held for sale (excluding leases)		1,049.5	439.6
Loans (excluding leases)		26,844.8	26,846.7
Securities purchased under agreement to resell		150.0
Investment securities		6,469.9	4,494.2
Indemnification assets		87.4	201.0
Other assets subject to fair value disclosure and unsecured counterparty receivables		542.2	712.2
Financial Liabilities
Deposits		(29,668.6)	(32,490.9)
Borrowings		(9,272.9)	(15,562.7)
Credit balances of factoring clients		(1,468.6)	(1,292.0)
Other liabilities subject to fair value disclosure		(725.2)	(1,003.6)
Agency claimed indemnification assets		28.9	108.0
Estimated Fair Value | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		68.5	94.7
Financial Liabilities
Derivative liabilities at fair value		(68.3)	(68.8)
Estimated Fair Value | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.2	16.9
Financial Liabilities
Derivative liabilities at fair value		(18.7)
Level 1 | Estimated Fair Value
Financial Assets
Cash and interest bearing deposits		1,718.7	6,430.6
Assets held for sale (excluding leases)		0.0	0.0
Loans (excluding leases)		0.0	0.0
Securities purchased under agreement to resell		0.0
Investment securities		199.2	200.4
Indemnification assets		0.0	0.0
Other assets subject to fair value disclosure and unsecured counterparty receivables		0.0	0.0
Financial Liabilities
Deposits		0.0	0.0
Borrowings		0.0	0.0
Credit balances of factoring clients		0.0	0.0
Other liabilities subject to fair value disclosure		0.0	0.0
Level 1 | Estimated Fair Value | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.0	0.0
Financial Liabilities
Derivative liabilities at fair value		0.0	0.0
Level 1 | Estimated Fair Value | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.0	0.0
Financial Liabilities
Derivative liabilities at fair value		0.0
Level 2 | Estimated Fair Value
Financial Assets
Cash and interest bearing deposits		0.0	0.0
Assets held for sale (excluding leases)		4.7	175.0
Loans (excluding leases)		624.3	390.3
Securities purchased under agreement to resell		150.0
Investment securities		5,583.3	3,199.6
Indemnification assets		0.0	0.0
Other assets subject to fair value disclosure and unsecured counterparty receivables		0.0	0.0
Financial Liabilities
Deposits		0.0	0.0
Borrowings		(8,281.7)	(14,457.8)
Credit balances of factoring clients		0.0	0.0
Other liabilities subject to fair value disclosure		0.0	0.0
Level 2 | Estimated Fair Value | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		68.4	94.7
Financial Liabilities
Derivative liabilities at fair value		(54.2)	(57.3)
Level 2 | Estimated Fair Value | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.2	16.9
Financial Liabilities
Derivative liabilities at fair value		(18.7)
Level 3 | Estimated Fair Value
Financial Assets
Cash and interest bearing deposits		0.0	0.0
Assets held for sale (excluding leases)		1,044.8	264.6
Loans (excluding leases)		26,220.5	26,456.4
Securities purchased under agreement to resell		0.0
Investment securities		687.4	1,094.2
Indemnification assets		87.4	201.0
Other assets subject to fair value disclosure and unsecured counterparty receivables		542.2	712.2
Financial Liabilities
Deposits		(29,668.6)	(32,490.9)
Borrowings		(991.2)	(1,104.9)
Credit balances of factoring clients		(1,468.6)	(1,292.0)
Other liabilities subject to fair value disclosure		(725.2)	(1,003.6)
Debt Securities AFS		385.8	485.5
Debt securities HFM			68.8
Non-marketable securities		301.2	256.4
Level 3 | Estimated Fair Value | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.1	0.0
Financial Liabilities
Derivative liabilities at fair value		(14.1)	(11.5)
Level 3 | Estimated Fair Value | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.0	0.0
Financial Liabilities
Derivative liabilities at fair value		0.0
Recurring
Financial Liabilities
Debt Securities AFS		6,123.6	3,674.1
Securities carried at fair value with changes recorded in net income		0.4	283.5
Recurring | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		68.5	94.7
Financial Liabilities
Derivative liabilities at fair value		(68.3)	(68.8)
Recurring | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.2	16.9
Financial Liabilities
Derivative liabilities at fair value		(18.7)
Recurring | Level 1
Financial Liabilities
Debt Securities AFS		199.0	200.1
Securities carried at fair value with changes recorded in net income		0.0	0.0
Recurring | Level 1 | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.0	0.0
Financial Liabilities
Derivative liabilities at fair value		0.0	0.0
Recurring | Level 1 | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.0	0.0
Recurring | Level 2
Financial Liabilities
Debt Securities AFS		5,538.8	2,988.5
Securities carried at fair value with changes recorded in net income		0.0	0.0
Recurring | Level 2 | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		68.4	94.7
Financial Liabilities
Derivative liabilities at fair value		(54.2)	(57.3)
Recurring | Level 2 | Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.2	16.9
Financial Liabilities
Derivative liabilities at fair value		(18.7)
Recurring | Level 3
Financial Liabilities
Debt Securities AFS		385.8	485.5
Securities carried at fair value with changes recorded in net income		0.4	283.5
Recurring | Level 3 | Non-Qualifying Hedges
Financial Assets
Derivative assets at fair value		0.1	0.0
Financial Liabilities
Derivative liabilities at fair value		(14.1)	(11.5)
Recurring | Level 3 | Qualifying Hedges
Financial Assets
Derivative assets at fair value		$ 0.0	$ 0.0

[1] The following table presents information on assets and liabilities related to Variable Interest Entities (VIEs) that are consolidated by the Company. The difference between VIE total assets and total liabilities represents the Company's interests in those entities, which were eliminated in consolidation. The assets of the consolidated VIEs will be used to settle the liabilities of those entities and, except for the Company's interest in the VIEs, are not available to the creditors of CIT or any affiliates of CIT.