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Commitments and Contingencies (Letters of Credit, Bonds, Self-Insurance) (Narrative) (Details) - USD ($) $ in Millions | Jun. 30, 2021 | Dec. 31, 2020
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Commitments and Contingencies [Line Items] |  |
Letters of credit issued | $ 123.7 | $ 151.8
Self-Insurance | Workers' Compensation, General and Automobile Policies |  |
Commitments and Contingencies [Line Items] |  |
Self-insurance reserve | 145.6 | 129.6
Self-Insurance | Workers' Compensation, General and Automobile Policies | Other Long-Term Liabilities |  |
Commitments and Contingencies [Line Items] |  |
Self-insurance reserve, non-current | 89.4 | 86.1
Self-Insurance | Employee Group Medical Claims |  |
Commitments and Contingencies [Line Items] |  |
Self-insurance reserve | 5.1 | 4.3
Performance and Payment Bonds |  |
Commitments and Contingencies [Line Items] |  |
Bonded projects, estimated costs to complete | 724.4 | 263.2
Performance and Payment Bonds | Subsidiaries |  |
Commitments and Contingencies [Line Items] |  |
Outstanding bonds, amount | 1,919.1 | 764.8
Performance and Payment Bonds | Subsidiaries | Corporate Joint Venture |  |
Commitments and Contingencies [Line Items] |  |
Outstanding bonds, amount | 115.0 |
Financial Guarantees | Self-Insurance | Workers' Compensation, General and Automobile Policies |  |
Commitments and Contingencies [Line Items] |  |
Letters of credit issued | 64.1 | 59.3
Surety Bonds | Self-Insurance | Workers' Compensation |  |
Commitments and Contingencies [Line Items] |  |
Outstanding bonds, amount | $ 37.4 | $ 37.4

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