Revenues - Topic 606 Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Trade receivables, net	$ 172.3	$ 201.8
Prepaid expenses and other current assets	67.3	44.6
Receivables from related parties	6.2	18.1
Computer software, net	405.6	416.8
Other non-current assets	286.9	240.1
Total assets	3,653.4	3,655.9	$ 3,762.0
Deferred revenues (current)	52.9	59.6
Deferred revenues (non-current)	106.8	100.7
Deferred income taxes, net	220.9	224.6
Deferred income taxes		224.6
Total liabilities	1,866.9	1,947.1
Retained earnings (accumulated deficit)	381.1	201.4
Total equity	1,786.5	1,708.8	$ 1,939.4	$ 1,845.0
Total liabilities and equity	3,653.4	3,655.9
ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Trade receivables, net	179.2	195.6
Prepaid expenses and other current assets	52.9	56.4
Receivables from related parties	11.0	14.4
Computer software, net	401.9	418.6
Other non-current assets	262.7	256.7
Total assets	3,622.8	3,676.2
Deferred revenues (current)	57.0	57.7
Deferred revenues (non-current)	102.5	107.5
Deferred income taxes, net	212.8
Deferred income taxes		228.8
Total liabilities	1,858.6	1,956.2
Retained earnings (accumulated deficit)	358.8	212.6
Total equity	1,764.2	1,720.0
Total liabilities and equity	3,622.8	3,676.2
ASU 2014-09 | Adjustments for ASC 606 Adoption [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Trade receivables, net	6.9	(6.2)
Prepaid expenses and other current assets	(14.4)	11.8
Receivables from related parties	4.8	(3.7)
Computer software, net	(3.7)	1.8
Other non-current assets	(24.2)	16.6
Total assets	(30.6)	20.3
Deferred revenues (current)	4.1	(1.9)
Deferred revenues (non-current)	(4.3)	6.8
Deferred income taxes, net	(8.1)
Deferred income taxes		4.2
Total liabilities	(8.3)	9.1
Retained earnings (accumulated deficit)	(22.3)	11.2
Total equity	(22.3)	11.2
Total liabilities and equity	$ (30.6)	$ 20.3