Significant Accounting Policies and Practices - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Parking services revenue
Revenues	$ 362.1	$ 392.7	$ 1,091.2	$ 1,198.1
Cost of parking services
Cost of parking services	317.1	346.8	955.6	1,054.2
Gross profit
Gross profit	45.0	45.9	135.6	143.9
Depreciation and amortization	4.2	4.9	12.7	16.3
Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	395.9		1,190.7
Cost of parking services
Cost of parking services	350.9		1,055.0
Gross profit
Gross profit	45.0		135.8
Depreciation and amortization	4.3		13.0
Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	(33.8)		(99.5)
Cost of parking services
Cost of parking services	(33.8)		(99.4)
Gross profit
Gross profit	0.0		(0.2)
Depreciation and amortization	(0.1)		(0.3)
Lease type contracts
Parking services revenue
Revenues	104.7	140.9	311.6	422.6
Cost of parking services
Cost of parking services	94.2	131.0	283.2	387.0
Gross profit
Gross profit	10.5	9.9	28.4	35.6
Lease type contracts | Accounting Standards Update 2017-10
Cost of parking services
Cost of parking services	33.8		99.4
Lease type contracts | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	138.5		411.1
Cost of parking services
Cost of parking services	128.0		382.6
Gross profit
Gross profit	10.5		28.5
Lease type contracts | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	(33.8)		(99.5)
Cost of parking services
Cost of parking services	(33.8)		(99.4)
Gross profit
Gross profit	0.0		(0.1)
Management type contracts
Parking services revenue
Revenues	82.6	86.7	264.8	262.8
Cost of parking services
Cost of parking services	48.1	50.7	157.6	154.5
Gross profit
Gross profit	34.5	36.0	107.2	108.3
Management type contracts | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	82.6		264.8
Cost of parking services
Cost of parking services	48.1		157.6
Gross profit
Gross profit	34.5		107.3
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		(0.1)
Lease and Management type contracts
Parking services revenue
Revenues	187.3	227.6	576.4	685.4
Cost of parking services
Cost of parking services	142.3	181.7	440.8	541.5
Lease and Management type contracts | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	221.1		675.9
Cost of parking services
Cost of parking services	176.1		540.2
Lease and Management type contracts | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	(33.8)		(99.5)
Cost of parking services
Cost of parking services	(33.8)		(99.4)
Reimbursed management type contract
Parking services revenue
Revenues	174.8	165.1	514.8	512.7
Cost of parking services
Cost of parking services	174.8	$ 165.1	514.8	$ 512.7
Reimbursed management type contract | Balances without Adoption of Topics 853 and 606 | Accounting Standards Update 2017-10 and 2014-09
Parking services revenue
Revenues	174.8		514.8
Cost of parking services
Cost of parking services	174.8		514.8
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