Railcar Leasing and Management Services Group - Selected consolidating income statement information for the Leasing Group (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 735.0	$ 606.9	$ 634.0	$ 533.2	$ 615.4	$ 655.7	$ 595.7	$ 530.6	$ 2,509.1	$ 2,397.4	$ 3,089.8
Operating profit:
Total operating profit	89.8	75.2	88.0	62.1	115.5	105.1	83.1	64.6	315.1	368.3	478.9
Selected expense information:
Depreciation									251.9	229.7	217.3
Selling, engineering, and administrative expenses	$ 72.0	$ 75.6	$ 75.6	$ 73.4	$ 88.5	$ 85.8	$ 85.8	$ 79.2	296.6	339.3	313.9
Interest:
Interest									179.3	184.0	181.9
Operating Segments
Revenues:
Total revenues									3,550.8	3,220.3	4,211.5
Operating profit:
Total operating profit									558.9	642.2	811.0
Selected expense information:
Depreciation									242.0	220.2	208.7
Railcar Leasing and Management Services Group
Revenues:
Total revenues									842.0	842.2	824.9
Selected expense information:
Depreciation									196.6	172.3	156.2
Railcar Leasing and Management Services Group | Operating Segments
Revenues:
Total revenues									$ 842.8	$ 843.2	827.0
Percent Change, Revenues									0.00%	2.00%
Operating profit:
Total operating profit									$ 351.1	$ 444.5	$ 360.1
Percentage Change, Operating profit									(21.00%)	23.40%
Operating profit margin:
Total operating profit margin									41.70%	52.70%	43.50%
Selected expense information:
Depreciation									$ 196.6	$ 172.3	$ 156.2
Percent Change, Depreciation									14.10%	10.30%
Maintenance and compliance									$ 99.3	$ 96.4	104.3
Percent Change, Maintenance									3.00%	(7.60%)
Rent									$ 42.4	$ 39.9	39.3
Percent Change, Rent									6.30%	1.50%
Selling, engineering, and administrative expenses									$ 51.1	$ 50.7	45.4
Selling, General, and Administrative Expense, Percent Change									0.80%	11.70%
Interest:
Interest									$ 142.3	$ 125.8	125.2
Percent Change, Total interest expense									13.10%	0.50%
Railcar Leasing and Management Services Group | Operating Segments | Leasing and management
Revenues:
Total revenues									$ 728.9	$ 743.6	700.9
Percent Change, Revenues									(2.00%)	6.10%
Operating profit:
Total operating profit									$ 291.8	$ 341.3	$ 312.5
Percentage Change, Operating profit									(14.50%)	9.20%
Operating profit margin:
Total operating profit margin									40.00%	45.90%	44.60%
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned one year or less at the time of sale
Revenues:
Total revenues									$ 113.9	$ 99.6	$ 126.1
Operating profit:
Total operating profit									21.5	19.7	34.1
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned more than one year at the time of sale
Operating profit:
Total operating profit									50.4	83.5	13.5
Railcar Leasing and Management Services Group | Operating Segments | Property Disposition Gain / Loss [Domain]
Operating profit:
Total operating profit									(12.6)	$ 0.0	$ 0.0
Capital lease obligations | Railcar Leasing and Management Services Group
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gain (Loss) on Disposition of Assets									$ 12.6