Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Asset Impairment Charges									$ 0.3	$ 6.6	$ 9.0
Nonoperating Income, Residual Sharing Income									2.5	1.9	2.5
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Amount									0.0	0.0	1.4
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									39.5	56.2	79.3
Revaluation of deferred tax liabilities									0.0	0.0	(9.4)
Total Revenues	$ 304.9	$ 304.4	$ 300.5	$ 299.4	$ 300.5	$ 298.8	$ 297.5	$ 305.3	1,209.2	1,202.1	1,175.1
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	17.8	48.2	37.0	47.2					125.3	145.2	170.7
Income from continuing operations					42.1	37.2	60.3	41.2	150.2	180.8	190.5
Total Discontinued Operations, Net of Taxes	0.0	(0.3)	2.3	(0.9)	14.5	7.9	7.7	0.3	1.1	30.4	20.8
Net Income	$ 17.8	$ 47.9	$ 39.3	$ 46.3	$ 56.6	$ 45.1	$ 68.0	$ 41.5	$ 151.3	$ 211.2	$ 211.3
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.51	$ 1.38	$ 1.06	$ 1.35	$ 1.21	$ 1.05	$ 1.68	$ 1.13	$ 4.30	$ 5.07	$ 5.07
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Basic Share	0	(0.01)	0.06	(0.02)	0.41	0.23	0.21	0.01	0.03	0.85	0.55
Earnings Per Share, Basic	0.51	1.37	1.12	1.33	1.62	1.28	1.89	1.14	4.33	5.92	5.62
Income (Loss) from Continuing Operations, Per Diluted Share	0.50	1.36	1.05	1.33	1.18	1.03	1.65	1.11	4.24	4.97	4.98
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Diluted Share	0	(0.01)	0.06	(0.02)	0.41	0.22	0.21	0.01	0.03	0.84	0.54
Earnings Per Share, Diluted	$ 0.50	$ 1.35	$ 1.11	$ 1.31	$ 1.59	$ 1.25	$ 1.86	$ 1.12	$ 4.27	$ 5.81	$ 5.52
Selected Quarterly Financial Data (unaudited)
Revenues	$ 304.9	$ 304.4	$ 300.5	$ 299.4	$ 300.5	$ 298.8	$ 297.5	$ 305.3	$ 1,209.2	$ 1,202.1	$ 1,175.1
Net income	$ 17.8	$ 47.9	$ 39.3	$ 46.3	$ 56.6	$ 45.1	$ 68.0	$ 41.5	$ 151.3	$ 211.2	$ 211.3
Share Data
Basic earnings per share (in dollars per share)	$ 0.51	$ 1.37	$ 1.12	$ 1.33	$ 1.62	$ 1.28	$ 1.89	$ 1.14	$ 4.33	$ 5.92	$ 5.62
Diluted earnings per share (in dollars per share)	$ 0.50	$ 1.35	$ 1.11	$ 1.31	$ 1.59	$ 1.25	$ 1.86	$ 1.12	$ 4.27	$ 5.81	$ 5.52
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 17.8	$ 48.2	$ 37.0	$ 47.2					$ 125.3	$ 145.2	$ 170.7
Total Discontinued Operations, Net of Taxes	$ 0.0	$ (0.3)	$ 2.3	$ (0.9)	$ 14.5	$ 7.9	$ 7.7	$ 0.3	$ 1.1	$ 30.4	$ 20.8
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.51	$ 1.38	$ 1.06	$ 1.35	$ 1.21	$ 1.05	$ 1.68	$ 1.13	$ 4.30	$ 5.07	$ 5.07
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Basic Share	0	(0.01)	0.06	(0.02)	0.41	0.23	0.21	0.01	0.03	0.85	0.55
Income (Loss) from Continuing Operations, Per Diluted Share	0.50	1.36	1.05	1.33	1.18	1.03	1.65	1.11	4.24	4.97	4.98
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Diluted Share	$ 0	$ (0.01)	$ 0.06	$ (0.02)	$ 0.41	$ 0.22	$ 0.21	$ 0.01	$ 0.03	$ 0.84	$ 0.54
Income from continuing operations					$ 42.1	$ 37.2	$ 60.3	$ 41.2	$ 150.2	$ 180.8	$ 190.5
Rail International [Member]
Asset Impairment Charges									0.0	0.0	3.9
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Total Revenues									258.1	227.7	217.5
Selected Quarterly Financial Data (unaudited)
Revenues									258.1	227.7	217.5
Portfolio Management [Member]
Asset Impairment Charges									0.0	6.2	4.5
Nonoperating Income, Residual Sharing Income									2.1	1.5	1.1
Total Revenues									17.0	9.9	16.1
Selected Quarterly Financial Data (unaudited)
Revenues									17.0	9.9	16.1
Rail North America [Member]
Asset Impairment Charges									0.3	0.4	0.6
Nonoperating Income, Residual Sharing Income									0.4	0.4	1.4
Total Revenues									934.1	964.5	941.5
Selected Quarterly Financial Data (unaudited)
Revenues									934.1	964.5	941.5
Canada Revenue Agency [Member]
Revaluation of deferred tax liabilities									$ 0.7	$ 2.8	$ 0.0