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Self-Insurance (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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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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