Changes in accumulated other comprehensive loss by component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Changes in accumulated other comprehensive loss by component
Balance at beginning of period			$ (139.3)
Other comprehensive income (loss):
Foreign currency translation adjustments	$ 1.0	$ 4.5	19.4	$ (30.6)
Net amount reclassified to earnings:
Tax expense	(18.4)	2.9	(16.8)	(1.7)
Total Other comprehensive income	1.0	4.8	19.1	(30.6)
Balance at end of period	(120.2)		(120.2)		$ (139.3)
Foreign currency translation
Changes in accumulated other comprehensive loss by component
Balance at beginning of period	(120.7)	(101.4)	(139.1)	(66.3)	(66.3)
Other comprehensive income (loss):
Foreign currency translation adjustments	1.0	4.5	19.4	(30.6)
Net amount reclassified to earnings:
Balance at end of period	(119.7)	(96.9)	(119.7)	(96.9)	(139.1)
Pension
Changes in accumulated other comprehensive loss by component
Balance at beginning of period	(0.4)	(2.1)	(0.4)	(2.1)	(2.1)
Net amount reclassified to earnings:
Balance at end of period	(0.4)	(2.1)	(0.4)	(2.1)	(0.4)
Cash flow hedges
Changes in accumulated other comprehensive loss by component
Balance at beginning of period	(0.1)	(0.2)	0.2	0.1	0.1
Other comprehensive income (loss):
Tax benefit (expense)	0.1	(0.1)	0.4	0.1
Total Other comprehensive income (loss) before reclassifications, net of tax	(0.2)	0.1	(0.7)	(0.2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0.2	0.2	0.4	0.2
Net change from periodic revaluations	(0.3)	0.2	(1.1)	(0.3)
Net amount reclassified to earnings:
Tax expense	(0.1)	(0.1)	(0.2)	(0.4)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0.2	0.2	0.4	0.2
Total Other comprehensive income		0.3	(0.3)
Balance at end of period	(0.1)	0.1	(0.1)	0.1	$ 0.2
Cash flow hedges | Interest rate swaps
Net amount reclassified to earnings:
Interest rate swaps	$ 0.3	$ 0.3	$ 0.6	$ 0.6