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Commitments and Contingencies (Letters of Credit, Bonds, Self-Insurance) (Narrative) (Details) - USD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
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