Accumulated other comprehensive loss - Schedule of Changes in Accumulated Other Comprehensive Loss by Component Net of Tax (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 1,683.6	$ 1,781.0	$ 1,732.8	$ 1,191.7
Other comprehensive loss before reclassifications		8.6	(1.5)	(96.6)	1.2
Amounts reclassified from accumulated other comprehensive loss		5.9	(2.7)	0.9	(5.5)
Net current period other comprehensive (loss) income		14.5	(4.2)	(95.7)	(7.5)
Ending balance		1,703.2	1,774.5	1,703.2	$ 1,774.5
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201802Member
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(489.5)	(376.5)	(379.3)	$ (373.2)
Impact due to adoption of ASU 2018-02	[1]						$ (3.2)
Ending balance		(475.0)	(380.7)	(475.0)	(380.7)
Accumulated other comprehensive loss | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Impact due to adoption of ASU 2018-02						$ (3.2)
Cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(31.5)	2.1	(15.4)	8.9
Other comprehensive loss before reclassifications		(11.1)	(13.1)	(22.2)	(18.6)
Amounts reclassified from accumulated other comprehensive loss		5.8	(2.8)	0.8	(5.6)
Net current period other comprehensive (loss) income		(5.3)	(15.9)	(21.4)	(22.7)
Ending balance		(36.8)	(13.8)	(36.8)	(13.8)
Cash flow hedges | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Impact due to adoption of ASU 2018-02						1.5
Defined benefit pension items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(1.0)	(1.1)	(1.0)	(1.1)
Other comprehensive loss before reclassifications		0.0	0.0	0.0	0.0
Amounts reclassified from accumulated other comprehensive loss		0.1	0.1	0.1	0.1
Net current period other comprehensive (loss) income		0.1	0.1	0.1	0.1
Ending balance		(0.9)	(1.0)	(0.9)	(1.0)
Defined benefit pension items | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Impact due to adoption of ASU 2018-02						0.0
Currency translation items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(457.0)	(377.5)	(362.9)	(381.0)
Other comprehensive loss before reclassifications		19.7	11.6	(74.4)	19.8
Amounts reclassified from accumulated other comprehensive loss		0.0	0.0	0.0	0.0
Net current period other comprehensive (loss) income		19.7	11.6	(74.4)	15.1
Ending balance		$ (437.3)	$ (365.9)	$ (437.3)	$ (365.9)
Currency translation items | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Impact due to adoption of ASU 2018-02						$ (4.7)

[1] Adjusted due to the adoption of ASU 2018-02 “Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” on January 1, 2019.