Restructuring Charges (Narrative) (Details) $ in Millions	3 Months Ended							12 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) Leases locomotives	Dec. 31, 2019 USD ($) locomotives	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) restructuring_plans	Dec. 31, 2018 USD ($)
Asset Impairment and Restructuring Costs [Line Items]
Payment of employer payroll taxes otherwise due in 2020 that were delayed due to CARES Act								$ 11.0
Percentage of payroll taxes delayed due to CARES Act that are due by December 31, 2021								50.00%
Percentage of payroll taxes delayed due to CARES Act that are due by December 31, 2022								50.00%
Decrease in revenue compared to same period in the prior year, percent								(8.00%)
Restructuring charges	$ 0.5	$ 10.5	$ 6.0	$ 38.3	$ 12.0	$ 51.0	$ 67.5	$ 17.0	$ 168.8	$ 0.0
Percentage of management employees irrevocably accepted into voluntary separation program		6.00%
PSR Initiatives [Member]
Asset Impairment and Restructuring Costs [Line Items]
Restructuring charges									$ 168.8
Number of separate restructuring plans approved by management | restructuring_plans									4
Number of leased locomotives purchased | locomotives			91
Amount paid by the company to purchase leased locomotives			$ 78.2
Number of existing leases that locomotives were a part of prior to purchase | Leases			2
Number of leased locomotives purchased that were impaired | locomotives				13
Workforce Reduction [Member]
Asset Impairment and Restructuring Costs [Line Items]
Restructuring charges								9.7	$ 7.0
Asset Impairments [Member]
Asset Impairment and Restructuring Costs [Line Items]
Restructuring charges								7.3	$ 157.8
Asset Impairments [Member] | PSR Initiatives [Member]
Asset Impairment and Restructuring Costs [Line Items]
Restructuring charges		$ 1.3	$ 6.0					$ 7.3