Business Segment Information (Segment Pre-Tax Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017		Jun. 30, 2016	Jun. 30, 2017		Jun. 30, 2016	Dec. 31, 2016
Segment Pre-tax Income (Loss)
Interest income	$ 478.2		$ 478.7	$ 933.9		$ 961.6
Interest (expense) benefit	(209.2)		(191.6)	(372.3)		(386.6)
Provision for credit losses	(4.4)		(23.3)	(54.1)		(112.8)
Rental income on operating leases	251.2		261.0	502.5		525.1
Other non-interest income	84.6		99.8	163.7		184.6
Depreciation on operating lease equipment	(77.4)		(63.1)	(150.9)		(124.4)
Maintenance and other operating lease expenses	(53.3)		(50.6)	(107.1)		(99.5)
Operating expenses / loss on debt extinguishment and deposit redemption	(460.4)		(311.7)	(772.0)		(643.4)
Income from continuing operations before benefit (provision) for income taxes	9.3		199.2	143.7		304.6
Select Period End Balances
Loans	29,031.7		30,093.8	29,031.7		30,093.8	$ 29,535.9
Credit balances of factoring clients	1,405.3		1,215.2	1,405.3		1,215.2	1,292.0
Assets held for sale	1,324.8	[1]	1,639.1	1,324.8	[1]	1,639.1	636.0	[1]
Operating lease equipment, net	6,736.0	[1]	7,179.1	6,736.0	[1]	7,179.1	$ 7,486.1	[1]
Corporate and Other [Member]
Segment Pre-tax Income (Loss)
Interest income	53.8		28.6	95.0		57.3
Interest (expense) benefit	(86.0)		(42.7)	(130.8)		(85.1)
Other non-interest income	3.9		13.4	5.7		17.5
Operating expenses / loss on debt extinguishment and deposit redemption	(185.9)		(25.7)	(221.2)		(62.7)
Income from continuing operations before benefit (provision) for income taxes	(214.2)		(26.4)	(251.3)		(73.0)
Commercial Banking [Member] | Operating Segments [Member]
Segment Pre-tax Income (Loss)
Interest income	316.6		323.4	624.1		647.3
Interest (expense) benefit	(127.8)		(130.3)	(247.6)		(260.4)
Provision for credit losses	0.2		(22.2)	(49.0)		(108.6)
Rental income on operating leases	251.2		257.0	502.5		517.3
Other non-interest income	74.8		68.0	147.1		126.0
Depreciation on operating lease equipment	(77.4)		(63.1)	(150.9)		(124.4)
Maintenance and other operating lease expenses	(53.3)		(50.6)	(107.1)		(99.5)
Operating expenses / loss on debt extinguishment and deposit redemption	(176.5)		(188.0)	(355.2)		(385.4)
Income from continuing operations before benefit (provision) for income taxes	207.8		194.2	363.9		312.3
Select Period End Balances
Loans	22,341.2		22,973.7	22,341.2		22,973.7
Credit balances of factoring clients	1,405.3		1,215.2	1,405.3		1,215.2
Assets held for sale	1,153.8		508.2	1,153.8		508.2
Operating lease equipment, net	6,736.0		7,179.1	6,736.0		7,179.1
Consumer Banking [Member] | Operating Segments [Member]
Segment Pre-tax Income (Loss)
Interest income	101.6		103.5	201.6		208.8
Interest (expense) benefit	9.6		(4.8)	16.1		(12.8)
Provision for credit losses	(4.6)		(1.1)	(5.1)		(4.2)
Other non-interest income	5.7		11.7	13.6		19.9
Operating expenses / loss on debt extinguishment and deposit redemption	(96.2)		(86.0)	(191.8)		(171.1)
Income from continuing operations before benefit (provision) for income taxes	16.1		23.3	34.4		40.6
Select Period End Balances
Loans	6,690.5		7,120.1	6,690.5		7,120.1
Assets held for sale	56.4		37.8	56.4		37.8
Non-Strategic Portfolios [Member] | Operating Segments [Member]
Segment Pre-tax Income (Loss)
Interest income	6.2		23.2	13.2		48.2
Interest (expense) benefit	(5.0)		(13.8)	(10.0)		(28.3)
Rental income on operating leases			4.0			7.8
Other non-interest income	0.2		6.7	(2.7)		21.2
Operating expenses / loss on debt extinguishment and deposit redemption	(1.8)		(12.0)	(3.8)		(24.2)
Income from continuing operations before benefit (provision) for income taxes	(0.4)		8.1	(3.3)		24.7
Select Period End Balances
Assets held for sale	$ 114.6		$ 1,093.1	$ 114.6		$ 1,093.1

[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.Assets Cash and interest bearing deposits, restricted$93.2 $99.9Total loans, net of allowance for loan losses181.4 300.5Operating lease equipment, net764.4 775.8Assets of discontinued operations— 2,321.7Total Assets$1,039.0 $3,497.9Liabilities Beneficial interests issued by consolidated VIEs (classified as long-term borrowings)$647.4 $770.0Liabilities of discontinued operations— 1,204.6Total Liabilities$647.4 $1,974.6