Discontinued Operations - Narrative (Details) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' Equity Note, Spinoff Transaction		$ (1,732.2)
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized		36.3
Arcosa TSA Net Payable	$ 10.4	10.4
Revenue from Related Parties	6.4
Related Party Transaction, Purchases from Related Party	25.6
Accounts Receivable, Related Parties	1.3	1.3
Accounts Payable, Related Parties	$ 10.6	10.6
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized		$ 31.2	$ 14.2