Self-Insurance (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Insurance [Line Items]
Self-insurance reserves - current portion	$ 774.5	$ 566.8
Self-insurance reserves - long-term portion	235.4	217.9
Self-insurance reserves [Member]
Insurance [Line Items]
Self-insurance reserves - current portion	29.5	27.2
Self-insurance reserves - long-term portion	48.7	48.7
Total self-insurance liabilities	$ 78.2	$ 75.9

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