Financial Data of Business Segments (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment									$ 12.0	$ 5.7	$ (0.5)
Number of business segments | Segment									4
Profitability
Lease revenue									$ 1,098.1	1,127.1	1,130.1
Marine operating revenue									193.4	199.3	235.0
Other revenue									85.4	91.9	84.8
Total Revenues	$ 352.8	$ 359.6	$ 348.4	$ 316.1	$ 362.1	$ 362.9	$ 358.9	$ 334.4	1,376.9	1,418.3	1,449.9
Maintenance expense									328.3	332.3	326.1
Marine operating expense									131.0	129.5	155.9
Depreciation									307.3	297.2	290.5
Operating lease expense									62.5	73.5	87.2
Other operating expense									34.4	43.8	38.4
Total Expenses									863.5	876.3	898.1
Net gain on asset dispositions									54.1	98.0	79.2
Interest expense, net									(160.5)	(148.1)	(155.1)
Other (expense) income									(11.1)	(11.8)	(13.2)
Share of affiliates' earnings (pre-tax)									55.9	53.1	45.4
Segment profit (loss)									451.8	533.2	508.1
SG&A									181.5	174.7	192.4
Income tax benefit									(243.7)	95.7	110.9
Net Income	342.1	49.0	$ 53.4	$ 57.5	30.9	$ 95.7	$ 61.2	$ 69.3	502.0	257.1	205.3
Disposition Gains on Owned Assets									44.1	49.7	90.3
Nonoperating Income, Residual Sharing Income									10.2	83.6	13.4
Nonremarketing Disposition Gain (Loss)									8.4	3.2	9.4
Asset Impairment Charges									8.6	38.5	33.9
Selected Balance Sheet Data
Investments in affiliated companies	441.0				387.0				441.0	387.0	348.5
Identifiable assets	7,422.4				7,105.4				7,422.4	7,105.4	6,894.2
Capital Expenditures
Portfolio investments and capital additions									$ (603.4)	$ (620.7)	$ (714.7)
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									5	5	5
Profitability
Lease revenue									$ 899.9	$ 935.1	$ 930.9
Marine operating revenue									0.0	0.0	0.0
Other revenue									77.5	83.4	75.9
Total Revenues									977.4	1,018.5	1,006.8
Maintenance expense									265.0	266.5	264.2
Marine operating expense									0.0	0.0	0.0
Depreciation									239.4	231.8	215.1
Operating lease expense									60.7	67.6	82.2
Other operating expense									28.7	34.1	26.2
Total Expenses									593.8	600.0	587.7
Net gain on asset dispositions									45.2	16.6	67.2
Interest expense, net									(121.2)	(110.1)	(102.1)
Other (expense) income									(5.9)	(3.6)	(5.2)
Share of affiliates' earnings (pre-tax)									(2.4)	0.5	0.5
Segment profit (loss)									299.3	321.9	379.5
Disposition Gains on Owned Assets									44.0	45.5	66.6
Nonoperating Income, Residual Sharing Income									0.6	0.8	0.8
Nonremarketing Disposition Gain (Loss)									5.2	1.5	2.3
Asset Impairment Charges									4.6	31.2	2.5
Selected Balance Sheet Data
Investments in affiliated companies	6.8				10.5				6.8	10.5	12.0
Identifiable assets	4,915.0				4,775.6				4,915.0	4,775.6	4,629.1
Capital Expenditures
Portfolio investments and capital additions									$ (460.9)	$ (495.6)	$ (524.5)
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									3	3	2
Profitability
Lease revenue									$ 190.3	$ 182.0	$ 172.9
Marine operating revenue									0.0	0.0	0.0
Other revenue									6.8	7.0	7.5
Total Revenues									197.1	189.0	180.4
Maintenance expense									41.1	47.2	39.6
Marine operating expense									0.0	0.0	0.0
Depreciation									48.9	45.5	43.7
Operating lease expense									0.0	0.0	0.0
Other operating expense									4.7	5.3	5.1
Total Expenses									94.7	98.0	88.4
Net gain on asset dispositions									3.1	1.1	6.8
Interest expense, net									(33.4)	(29.7)	(22.4)
Other (expense) income									(3.2)	0.8	(6.0)
Share of affiliates' earnings (pre-tax)									(0.1)	(0.2)	(0.3)
Segment profit (loss)									68.8	63.0	70.1
Disposition Gains on Owned Assets									0.1	0.0	0.0
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)									3.3	1.7	7.2
Asset Impairment Charges									0.3	0.6	0.4
Selected Balance Sheet Data
Investments in affiliated companies	0.0				1.2				0.0	1.2	1.4
Identifiable assets	1,332.9				1,128.7				1,332.9	1,128.7	1,117.6
Capital Expenditures
Portfolio investments and capital additions									$ (90.9)	$ (87.1)	$ (148.0)
ASC [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									1.5	1.5	1.5
Profitability
Lease revenue									$ 4.1	$ 4.2	$ 4.1
Marine operating revenue									168.4	150.0	166.1
Other revenue									0.0	0.0	0.0
Total Revenues									172.5	154.2	170.2
Maintenance expense									22.2	18.6	22.3
Marine operating expense									106.2	96.7	107.2
Depreciation									12.0	12.9	14.3
Operating lease expense									1.8	6.0	5.2
Other operating expense									0.0	0.0	0.0
Total Expenses									142.2	134.2	149.0
Net gain on asset dispositions									(1.9)	0.0	(0.1)
Interest expense, net									(5.2)	(4.5)	(5.3)
Other (expense) income									1.3	(5.4)	(0.7)
Share of affiliates' earnings (pre-tax)									0.0	0.0	0.0
Segment profit (loss)									24.5	10.1	15.1
Disposition Gains on Owned Assets									(1.8)	0.0	0.0
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)									(0.1)	0.0	(0.1)
Asset Impairment Charges									0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0				0.0				0.0	0.0	0.0
Identifiable assets	286.7				278.8				286.7	278.8	284.7
Capital Expenditures
Portfolio investments and capital additions									$ (14.0)	$ (9.1)	$ (20.3)
Portfolio Management [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									1	1	3
Profitability
Lease revenue									$ 3.8	$ 5.8	$ 22.2
Marine operating revenue									25.0	49.3	68.9
Other revenue									1.1	1.5	1.4
Total Revenues									29.9	56.6	92.5
Maintenance expense									0.0	0.0	0.0
Marine operating expense									24.8	32.8	48.7
Depreciation									7.0	7.0	17.4
Operating lease expense									0.0	0.0	0.0
Other operating expense									1.0	4.4	7.1
Total Expenses									32.8	44.2	73.2
Net gain on asset dispositions									7.7	80.3	5.3
Interest expense, net									(9.2)	(8.6)	(20.0)
Other (expense) income									2.3	0.0	0.0
Share of affiliates' earnings (pre-tax)									58.4	52.8	45.2
Segment profit (loss)									56.3	136.9	49.8
Disposition Gains on Owned Assets									1.8	4.2	23.7
Nonoperating Income, Residual Sharing Income		$ 30.3							9.6	82.8	12.6
Nonremarketing Disposition Gain (Loss)									0.0	0.0	0.0
Asset Impairment Charges									3.7	6.7	31.0
Selected Balance Sheet Data
Investments in affiliated companies	434.2				375.3				434.2	375.3	335.1
Identifiable assets	582.8				593.5				582.8	593.5	636.5
Capital Expenditures
Portfolio investments and capital additions									(36.6)	(25.0)	(18.4)
Other [Member]
Profitability
Lease revenue									0.0	0.0	0.0
Marine operating revenue									0.0	0.0	0.0
Other revenue									0.0	0.0	0.0
Total Revenues									0.0	0.0	0.0
Maintenance expense									0.0	0.0	0.0
Marine operating expense									0.0	0.0	0.0
Depreciation									0.0	0.0	0.0
Operating lease expense									0.0	(0.1)	(0.2)
Other operating expense									0.0	0.0	0.0
Total Expenses									0.0	(0.1)	(0.2)
Net gain on asset dispositions									0.0	0.0	0.0
Interest expense, net									8.5	4.8	(5.3)
Other (expense) income									(5.6)	(3.6)	(1.3)
Share of affiliates' earnings (pre-tax)									0.0	0.0	0.0
Segment profit (loss)									2.9	1.3	(6.4)
Disposition Gains on Owned Assets									0.0	0.0	0.0
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)									0.0	0.0	0.0
Asset Impairment Charges									0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0				0.0				0.0	0.0	0.0
Identifiable assets	$ 305.0				$ 328.8				305.0	328.8	226.3
Capital Expenditures
Portfolio investments and capital additions									(1.0)	(3.9)	(3.5)
Parent [Member]
Profitability
Income tax benefit									$ (231.7)	$ 101.4	110.4
Cardinal Marine [Domain]
Profitability
Asset Impairment Charges											19.0
Cardinal Marine [Domain] | Portfolio Management [Member]
Profitability
Asset Impairment Charges											$ 19.0