Derivative instruments and hedging activities - Fair Value by Balance Sheet Location (Details) - Interest rate swaps - Designated as Hedging Instrument - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Other Current Assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 0.0	$ 0.0
Other Assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.0	0.0
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	5.6	0.0
Other Liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 11.9	$ 2.0