Retirement, Postretirement And Other Benefit Plans (Retirement and Postretirement Benefit Plans - Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Interest credit for accumulated balances		2.61%	2.55%
Effect of one percent increase in assumed healthcare trend rates on postretirement benefit obligation	$ 0.7
Effect of one percent decrease in assumed healthcare trend rates on postretirement benefit obligation	0.6
Cost of defined contribution plans	18.7	$ 15.8	$ 19.0
Non-U.S.
Defined Benefit Plan Disclosure [Line Items]
Expected future contributions for defined benefit plans in next fiscal year	10.0
Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Actuarial gain (loss)	(9.5)	(4.7)
Net losses (gains) recognized in AOCI before taxes	(18.6)	(7.9)	18.3
Gain (loss) amortized from AOCI into net periodic benefit cost	$ (1.5)	$ (2.9)	(2.6)
Discount rate	3.45%	3.73%
Expected service cost (credit) to be amortized from AOCI into net periodic benefit cost in the next fiscal year	$ 1.2
Direct investments in equity securities of CIT or its subsidiaries	0
Retirement Benefits | Minimum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	15.00%
Retirement Benefits | Minimum | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	35.00%
Retirement Benefits | Minimum | Global Asset Allocations
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	15.00%
Retirement Benefits | Minimum | Hedge Fund, measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	5.00%
Retirement Benefits | Maximum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	35.00%
Retirement Benefits | Maximum | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	65.00%
Retirement Benefits | Maximum | Global Asset Allocations
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	25.00%
Retirement Benefits | Maximum | Hedge Fund, measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Asset allocation percentage allowed by asset allocation policy	10.00%
Pension Plan and Supplemental Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Interest credit for accumulated balances	2.84%
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Actuarial gain (loss)	$ (0.5)	$ (0.2)
Expected recognition of gain (loss) next fiscal year	0.4
Net losses (gains) recognized in AOCI before taxes	2.1	2.1	(0.7)
Gain (loss) amortized from AOCI into net periodic benefit cost	$ 1.1	$ 0.7	$ 0.3
Discount rate	3.50%	3.75%
Expected service cost (credit) to be amortized from AOCI into net periodic benefit cost in the next fiscal year	$ 0.5