Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended							12 Months Ended
	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	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Mexican fuel excise tax credit, income tax expense reduction, net				$ 4.2	$ 3.7	$ (1.9)	$ 6.8
U.S. corporate income tax rate								21.00%	21.00%	21.00%
GILTI tax expense (benefit) recognized by the Company	$ (4.2)	$ 2.0	$ 2.2					$ (14.5)	$ 2.7	$ 11.8
KCSM [Member] | Long-Term Asset [Member]
Income Tax Disclosure [Line Items]
Refundable Mexican value added tax								103.1
KCSM [Member] | Short-Term Asset [Member]
Income Tax Disclosure [Line Items]
Refundable Mexican value added tax				$ 60.2					60.2
Foreign Tax Authority [Member] | Mexican Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryover, amount								9.3
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Disclosure [Line Items]
U.S. corporate income tax rate										21.00%	35.00%
GILTI tax expense (benefit) recognized by the Company								$ (14.5)
Percent dividends received deduction provided for in Tax Reform Act								100.00%
State and Local Jurisdiction [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryover, amount								$ 367.7
Net operating loss carryover, deferred tax asset								$ 22.0
State and Local Jurisdiction [Member] | Minimum [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryover, period								10 years
State and Local Jurisdiction [Member] | Maximum [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryover, period								20 years
Income Tax Expense [Member] | Foreign Tax Authority [Member] | Mexican Tax Authority [Member]
Income Tax Disclosure [Line Items]
Mexican fuel excise tax credit, income tax expense reduction, net									$ 12.8