Revenue (Tables)

6 Months Ended

Jun. 30, 2019

Revenue from Contract with Customer [Abstract]

Schedule of remaining performance obligation

The Company expects to recognize the remaining performance obligations as revenue in future periods as follows:

(millions) (unaudited)	Remaining Performance Obligations
2019	$	36.0
2020	48.4
2021	28.5
2022	13.7
2023	9.6
2024 and thereafter	9.7
Total	$	145.9

Schedule of contract with customer, asset and liability

The following table provides information about changes to contract liability balances for the six-month periods ended June 30, 2019 and 2018:

	Six Months Ended
(millions) (unaudited)	June 30, 2019			June 30, 2018
Balance, beginning of period	$	19.1		$	20.5
Additional contract liabilities	81.6			87.7
Recognition of revenue from contract liabilities	(85.8		)	(92.7		)
Balance, end of period	$	14.9		$	15.5

The following table provides information about accounts receivable, contract assets and contract liabilities with customers and clients as of June 30, 2019 (unaudited) and December 31, 2018:

(millions)	June 30, 2019			December 31, 2018
Accounts receivable	$	150.3		$	139.3
Contract asset	$	11.8		$	11.4
Contract liability	$	(14.9	)	$	(19.1	)

The following table provides information about changes to contract asset balances for the six-month periods ended June 30, 2019 and 2018:

	Six Months Ended
(millions) (unaudited)	June 30, 2019			June 30, 2018
Balance, beginning of period	$	11.4		$	12.2
Additional contract assets	64.7			68.4
Reclassification to accounts receivable	(64.3		)	(69.6		)
Balance, end of period	$	11.8		$	11.0

Schedule of amortization expense related to cost of contracts

The table below shows amortization expense related to cost of contracts for the three and six months ended June 30, 2019 and 2018. Amortization expense of cost of contracts related to service concession arrangements within the scope of Topic 853 is recorded as a reduction of revenue and was not significant for the three and six months ended June 30, 2019 and 2018, respectively.

	Three Months Ended				Six Months Ended
(millions) (unaudited)	June 30, 2019		June 30, 2018		June 30, 2019		June 30, 2018
Amortization expense related to cost of contract included in depreciation and amortization	$	0.3	$	0.8	$	0.6	$	1.5