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Commitments and Contingencies (Other Commitments and Contingencies) (Narrative) (Details) - USD ($) $ in Millions			3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2016	Nov. 30, 2011
Central States Southeast And Southwest Areas Pension Fund [Member] \| Multiemployer Plans, Pension [Member]
Commitments and Contingencies [Line Items]
Multiemployer plans, withdrawal obligation		$ 3.0		$ 6.4
Multiemployer plans, withdrawal obligation, payments			$ 3.0
Uninsured Risk [Member] \| Workers Compensation, General and Automobile Policies [Member]
Commitments and Contingencies [Line Items]
Self insurance reserve	$ 76.4	76.1	76.4
Uninsured Risk [Member] \| Workers Compensation, General and Automobile Policies [Member] \| Other Long-Term Liabilities [Member]
Commitments and Contingencies [Line Items]
Self insurance reserve, non-current	46.6	47.5	46.6
Uninsured Risk [Member] \| Workers Compensation, General and Automobile Policies [Member] \| Other Long-Term Assets [Member] \| Cash [Member]
Commitments and Contingencies [Line Items]
Cash collateral deposited with insurance carriers	1.3	1.3	1.3
Uninsured Risk [Member] \| Employee Group Medical Claims Policies [Member]
Commitments and Contingencies [Line Items]
Self insurance reserve	2.0	1.6	2.0
Performance and Payment Bonds [Member]
Commitments and Contingencies [Line Items]
Outstanding bonds, amount	147.8	539.3	147.8
Performance and Payment Bonds [Member] \| Estimate [Member]
Commitments and Contingencies [Line Items]
Bonded projects, costs to complete	21.6	36.0
Surety Bond [Member] \| Uninsured Risk [Member] \| Workers Compensation [Member]
Commitments and Contingencies [Line Items]
Outstanding bonds, amount	13.4	13.4	13.4
Credit Facility [Member]
Commitments and Contingencies [Line Items]
Letters of credit issued	403.8	292.8	403.8
Credit Facility [Member] \| Financial Guarantees [Member] \| Uninsured Risk [Member] \| Workers Compensation, General and Automobile Policies [Member]
Commitments and Contingencies [Line Items]
Letters of credit issued	$ 83.2	$ 83.2	$ 83.2