Significant Accounting Policies and Practices - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Parking services revenue
Revenues	$ 362.2	$ 403.5	$ 729.0	$ 805.4
Cost of parking services
Cost of parking services	311.1	346.0	638.4	707.4
Gross profit
Gross profit	51.1	57.5	90.6	98.0
Depreciation and amortization	4.5	4.8	8.5	11.4
Accounting Standards Update 2017-10
Gross profit
Expenses for contractual agreement	34.1		65.6
Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	396.3		794.7
Cost of parking services
Cost of parking services	345.2		704.0
Gross profit
Gross profit	51.1		90.7
Depreciation and amortization	4.6		8.6
Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	(34.1)		(65.7)
Cost of parking services
Cost of parking services	(34.1)		(65.6)
Gross profit
Gross profit	0.0		(0.1)
Depreciation and amortization	(0.1)		(0.1)
Lease type contracts
Parking services revenue
Revenues	107.4	150.9	206.9	281.7
Cost of parking services
Cost of parking services	94.5	130.2	189.0	256.0
Gross profit
Gross profit	12.9	20.7	17.9	25.7
Lease type contracts | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	141.5		272.6
Cost of parking services
Cost of parking services	128.6		254.6
Gross profit
Gross profit	12.9		18.0
Lease type contracts | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	(34.1)		(65.7)
Cost of parking services
Cost of parking services	(34.1)		(65.6)
Gross profit
Gross profit	0.0		(0.1)
Management type contracts
Parking services revenue
Revenues	87.7	84.0	182.2	176.1
Cost of parking services
Cost of parking services	49.5	47.2	109.5	103.8
Gross profit
Gross profit	38.2	36.8	72.7	72.3
Management type contracts | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	87.7		182.2
Cost of parking services
Cost of parking services	49.5		109.5
Gross profit
Gross profit	38.2		72.7
Management type contracts | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	0.0		0.0
Cost of parking services
Cost of parking services	0.0		0.0
Gross profit
Gross profit	0.0		0.0
Cost of parking services
Parking services revenue
Revenues	195.1	234.9	389.1	457.8
Cost of parking services
Cost of parking services	144.0	177.4	298.5	359.8
Cost of parking services | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	229.2		454.8
Cost of parking services
Cost of parking services	178.1		364.1
Cost of parking services | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	(34.1)		(65.7)
Cost of parking services
Cost of parking services	(34.1)		(65.6)
Reimbursed management type contract
Parking services revenue
Revenues	167.1	168.6	339.9	347.6
Cost of parking services
Cost of parking services	167.1	$ 168.6	339.9	$ 347.6
Reimbursed management type contract | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	167.1		339.9
Cost of parking services
Cost of parking services	167.1		339.9
Reimbursed management type contract | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	0.0		0.0
Cost of parking services
Cost of parking services	$ 0.0		$ 0.0