Railcar Leasing and Management Services Group - Selected consolidating income statement information for the Leasing Group (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Revenues	$ 930.9	$ 973.6	$ 2,704.5	$ 2,756.4
Operating profit:
Total operating profit	78.9	152.4	303.0	402.9
Select expense information:
Depreciation			234.0	220.7
Interest	42.8	46.8	132.9	137.5
Operating Segments
Revenues:
Revenues	1,181.0	1,199.4	3,571.1	3,404.6
Operating profit:
Total operating profit	137.6	208.6	498.2	579.5
Railcar Leasing and Management Services Group
Revenues:
Revenues	227.2	274.9	614.7	645.4
Railcar Leasing and Management Services Group | Leasing and management
Revenues:
Revenues	175.9	188.5	534.7	552.4
Railcar Leasing and Management Services Group | Railcars owned one year or less at the time of sale
Revenues:
Revenues	51.6	86.6	80.8	93.7
Railcar Leasing and Management Services Group | Operating Segments
Revenues:
Revenues	$ 227.5	275.1	$ 615.5	646.1
Percent Change, Revenues	(17.30%)		(4.70%)
Operating profit:
Total operating profit	$ 92.2	$ 120.6	$ 255.1	$ 316.4
Percent Change, Operating Profit	(23.50%)		(19.40%)
Operating profit margin:
Total operating profit margin	40.50%	43.80%	41.40%	49.00%
Select expense information:
Depreciation	$ 48.8	$ 43.3	$ 140.9	$ 128.5
Percent Change, Depreciation	12.70%		9.60%
Maintenance costs	$ 24.1	25.0	$ 75.5	69.4
Percent Change, Maintenance	(3.60%)		8.80%
Rent	$ 9.7	10.0	$ 29.7	30.0
Percent Change, Rent	(3.00%)		(1.00%)
Interest	$ 37.4	32.1	$ 101.2	94.0
Percent Change, Interest	16.50%		7.70%
Railcar Leasing and Management Services Group | Operating Segments | Leasing and management
Revenues:
Revenues	$ 175.9	188.5	$ 534.7	552.4
Percent Change, Revenues	(6.70%)		(3.20%)
Operating profit:
Total operating profit	$ 69.7	$ 86.2	$ 216.6	$ 256.8
Percent Change, Operating Profit	(19.10%)		(15.70%)
Operating profit margin:
Total operating profit margin	39.60%	45.70%	40.50%	46.50%
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned one year or less at the time of sale
Revenues:
Revenues	$ 51.6	$ 86.6	$ 80.8	$ 93.7
Operating profit:
Total operating profit	13.1	17.9	17.5	19.4
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned more than one year at the time of sale
Operating profit:
Total operating profit	$ 9.4	$ 16.5	$ 21.0	$ 40.2