Accounts Receivable, Net of Allowance (Tables) - Accounts Receivable [Member]

12 Months Ended

Dec. 31, 2017

Schedule of Accounts Receivable, Net of Allowance [Line Items]

Schedule of Accounts Receivable, Net of Allowance

The following table provides details of accounts receivable, net of allowance, as of the dates indicated (in millions):

	December 31,
	2017			2016
Contract billings	$	683.9		$	564.2
Retainage	323.1			268.6
Costs and earnings in excess of billings	599.2			331.6
Accounts receivable, gross	$	1,606.2		$	1,164.4
Less allowance for doubtful accounts	(8.2		)	(8.4		)
Accounts receivable, net	$	1,598.0		$	1,156.0

Schedule of Activity, Allowance for Doubtful Accounts

Activity in the allowance for doubtful accounts for the periods indicated is as follows (in millions):

	For the Years Ended December 31,
	2017			2016
Allowance for doubtful accounts at beginning of year	$	8.4		$	7.7
Provision for doubtful accounts	2.6			2.9
Amounts charged against the allowance	(2.8		)	(2.2		)
Allowance for doubtful accounts at end of year	$	8.2		$	8.4