Quarterly Financial Data Items affecting quarter results (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
After-tax restructuring and related costs	$ 1.7	$ 2.7	$ 7.6	$ 0.2	$ 0.9	$ 2.2	$ 2.2	$ 3.5
After-tax corporate development and related costs		0.3	0.3	0.1	0.7	1.8	2.7	$ 3.2
income tax expense associated with uncertain tax deductions			4.1
after tax credit facility refinancing-related costs			(2.0)
Adjustment to Tax Cuts And Jobs Act of 2017 Incomplete Accounting Transition Tax For Accumulated Foreign Earnings Provisional Income Tax Expense (Benefit)		(1.6)
Tax adjustments associated with prior period	1.4
After-tax gain on sale of investment	1.0						$ 1.0
Unrecognized Tax Benefits, Period Increase (Decrease)						$ 3.3
After tax reduction to other expense					8.9
After tax U.K. coal restructuring and related costs					1.2
Australian Operations [Member]
after tax gain on settlement		$ 0.3	2.3
After tax asset impairment and related charges					1.8
Internal Revenue Service (IRS) [Member]
Tax benefit associated with the United States Short Line Tax Credit				$ 31.6
Tax Cuts And Jobs Act of 2017 Incomplete Accounting Provisional Income Tax Expense (Benefit)					$ 372.0
ERS Railways [Member]
Loss on Disposition of Business			$ (1.4)						$ (1.4)
Canada [Member]
After tax lease return costs	$ 1.5