Significant Accounting Policies and Practices - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Services revenue									$ 1,468.4
Cost of services	$ 328.8	$ 317.1	$ 311.1	$ 327.4	$ 351.0	$ 346.8	$ 346.0	$ 361.4	1,284.4	$ 1,405.2	$ 1,392.0
Gross profit	48.5	45.0	51.1	39.4	41.4	45.9	57.5	40.5	184.0	185.3	176.4
Depreciation and amortization	5.2	4.2	4.5	4.0	4.7	4.9	4.8	6.6	17.9	21.0	33.7
Balances without Adoption of Topics 606 and 853
Disaggregation of Revenue [Line Items]
Services revenue									1,602.2
Cost of services									1,417.8
Gross profit									184.3
Depreciation and amortization									18.2
Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Disaggregation of Revenue [Line Items]
Services revenue									(133.8)
Cost of services									(133.4)
Gross profit									(0.3)
Depreciation and amortization									(0.3)
Lease type contracts
Disaggregation of Revenue [Line Items]
Services revenue									413.9
Cost of services	94.3	94.2	94.5	94.6	131.4	131.0	130.2	125.8	377.6	518.4	505.6
Gross profit	8.0	10.5	12.9	4.9	9.1	9.9	20.7	5.0	36.3	44.7	39.4
Lease type contracts | Accounting Standards Update 2017-10
Disaggregation of Revenue [Line Items]
Cost of services									133.4
Lease type contracts | Balances without Adoption of Topics 606 and 853
Disaggregation of Revenue [Line Items]
Services revenue									547.5
Cost of services									511.0
Gross profit									36.5
Lease type contracts | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Disaggregation of Revenue [Line Items]
Services revenue									(133.6)
Cost of services									(133.4)
Gross profit									(0.2)
Management type contracts
Disaggregation of Revenue [Line Items]
Services revenue									361.5
Cost of services	56.3	48.1	49.5	59.9	53.1	50.7	47.2	56.6	213.8	207.6	209.8
Gross profit	40.5	34.5	38.2	34.5	32.3	36.0	36.8	35.5	147.7	140.6	137.0
Management type contracts | Balances without Adoption of Topics 606 and 853
Disaggregation of Revenue [Line Items]
Services revenue									361.7
Cost of services									213.8
Gross profit									147.8
Management type contracts | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Disaggregation of Revenue [Line Items]
Services revenue									(0.2)
Cost of services									0.0
Gross profit									(0.1)
Lease And Management Type Contracts
Disaggregation of Revenue [Line Items]
Services revenue									775.4
Cost of services									591.4	726.0	715.4
Lease And Management Type Contracts | Balances without Adoption of Topics 606 and 853
Disaggregation of Revenue [Line Items]
Services revenue									909.2
Cost of services									724.8
Lease And Management Type Contracts | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Disaggregation of Revenue [Line Items]
Services revenue									(133.8)
Cost of services									(133.4)
Reimbursed management type contract revenue
Disaggregation of Revenue [Line Items]
Services revenue									693.0
Cost of services	$ 178.2	$ 174.8	$ 167.1	$ 172.9	$ 166.5	$ 165.1	$ 168.6	$ 179.0	693.0	$ 679.2	$ 676.6
Reimbursed management type contract revenue | Balances without Adoption of Topics 606 and 853
Disaggregation of Revenue [Line Items]
Services revenue									693.0
Cost of services									693.0
Reimbursed management type contract revenue | Impact of Adoption Increase/(Decrease) | Accounting Standards Update 2017-10 and 2014-09
Disaggregation of Revenue [Line Items]
Services revenue									0.0
Cost of services									$ 0.0