Commitments and Contingencies (Details 2) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012 item
Commitments and Contingencies
Number of multi-employer pension plans, the withdrawal of which could result in assessment of liabilities for additional contributions related to the underfunding of plans, minimum	1
Potential number of litigation claims in which an adverse outcome could result, minimum	1
Insurance and Claims Accruals
Commitments and Contingencies
Deductible per claim, once a policy's claim aggregate is reached per line of coverage	0.5
Deductible under health insurance benefits for qualified individuals	0.1
Insurance and Claims Accruals | Minimum
Commitments and Contingencies
Deductible per claim for each line of coverage, until claim aggregate is reached	1.0
Surety bonds
Commitments and Contingencies
Aggregate original face amount of outstanding bonds issued by the surety	917.6
Estimated remaining cost to complete bonded projects	387.0