Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	$ 1,750.9
Balance at the end of the period	2,395.2	$ 1,750.9
Foreign Currency Translation
Changes in accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(230.0)	(113.5)	$ (51.7)
Other comprehensive income (loss) before reclassifications	96.0	(116.5)	(61.8)
Net current period other comprehensive income (loss)	96.0	(116.5)	(61.8)
Balance at the end of the period	(134.0)	(230.0)	(113.5)
Other
Changes in accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(20.7)	(9.0)	(1.6)
Other comprehensive income (loss) before reclassifications	8.2	(11.7)	(7.4)
Net current period other comprehensive income (loss)	8.2	(11.7)	(7.4)
Balance at the end of the period	(12.5)	(20.7)	(9.0)
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(250.7)	(122.5)	(53.3)
Other comprehensive income (loss) before reclassifications	104.2	(128.2)	(69.2)
Net current period other comprehensive income (loss)	104.2	(128.2)	(69.2)
Balance at the end of the period	(146.5)	(250.7)	(122.5)
Amounts reclassified from accumulated other comprehensive income, tax provision	$ 0.0	$ 0.0	$ 0.0