Accumulated other comprehensive loss - Summary of amounts reclassified from accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	$ 29.1	$ 34.8
Income tax benefit	0.3	23.3
Net income (loss)	55.9	(63.9)
Cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income tax benefit	2.2	1.0
Net income (loss)	(5.0)	(2.8)
Cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	0.9	(3.8)
Cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income | Currency Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	$ (8.1)	$ 0.0