Revenue (Narrative) (Details) $ in Billions	9 Months Ended
	Sep. 30, 2018 USD ($)
Civil [Member]
Revenue, Remaining Performance Obligation, Amount	$ 4.2
Civil [Member] | Minimum [Member[
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Range	3 years
Civil [Member] | Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Range	5 years
Building [Member]
Revenue, Remaining Performance Obligation, Amount	$ 2.1
Specialty Contractors [Member]
Revenue, Remaining Performance Obligation, Amount	$ 1.7
Building And Specialty Contractors [Member] | Minimum [Member[
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Range	1 year
Building And Specialty Contractors [Member] | Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Range	3 years