Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Net revenue recognized related to performance obligations satisfies (or partially satisfied) in prior periods	$ 55.3	$ 54.2	$ 167.4	$ 164.1
Civil
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations revenue amount	4,500.0	4,700.0	$ 4,500.0	4,700.0
Civil | Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations revenue period			3 years
Civil | Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations revenue period			5 years
Building
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations revenue amount	2,300.0	2,300.0	$ 2,300.0	2,300.0
Specialty Contractors
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations revenue amount	$ 1,100.0	$ 1,300.0	$ 1,100.0	$ 1,300.0
Building and Specialty Contractors | Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations revenue period			1 year
Building and Specialty Contractors | Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations revenue period			3 years