Discontinued Operations (Narrative) (Details) - USD ($) $ in Millions				3 Months Ended			9 Months Ended
		May 16, 2017	Apr. 04, 2017	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio of reverse mortgages	[1]			$ 28,085.8			$ 28,085.8		$ 29,103.3
Settled Litigation | HUD OIG Investigation | Unfavorable Regulatory Action
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Amount of settlement		$ 89.0
Reverse Mortgage | Operating Segments | Consumer Banking | One West Transaction
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio of reverse mortgages				862.0			862.0
Other real estate owned assets				25.0			25.0
Commercial Air | Discontinued Operations, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase price			$ 10,400.0
Pre-tax gain from sale			$ 146.0
Financial Freedom | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (decrease) increase to servicing-related reserve						$ 230.0		$ 230.0
Financial Freedom | Discontinued Operations | Settled Litigation | HUD OIG Investigation | Unfavorable Regulatory Action
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Amount of settlement					$ 89.0
Financial Freedom | Discontinued Operations | Residential Mortgage
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reduction in indemnification receivable					77.0		77.0
Indemnification receivable from the FDIC				29.0			29.0
Net release of curtailment reserve				111.0	111.0
Increase in other servicing related reserves				40.0	40.0
Write-down of servicing operations					54.0
Impairment of mortgage servicing rights liability				$ 50.0	$ 50.0	$ 19.0		$ 19.0
Net (decrease) increase to servicing-related reserve							$ (102.0)

[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.Assets Cash and interest bearing deposits, restricted$88.3 $99.9Total loans, net of allowance for loan losses146.8 300.5Operating lease equipment, net759.9 775.8Assets of discontinued operations— 2,321.7Total Assets$995.0 $3,497.9Liabilities Beneficial interests issued by consolidated VIEs (classified as long-term borrowings)$603.9 $770.0Liabilities of discontinued operations— 1,204.6Total Liabilities$603.9 $1,974.6