Income taxes - Deferred tax asset, net of valuation allowance and Uncertain tax positions (Details) $ in Millions	Mar. 31, 2020 USD ($)
Income taxes
Net deferred tax liability, net of valuation allowance	$ 12.5
Other net deferred tax liabilities	10.2
Uncertain tax positions
Total reserve for unrecognized tax benefits	42.8
Reversal of reserves for unrecognized tax benefits on permanent differences and interest and penalties	42.6
Reversal of reserves for unrecognized tax benefits on temporary differences	0.2
U.S. subsidiaries
Income taxes
Net deferred tax assets	27.0
Luxembourg subsidiaries
Income taxes
Net deferred tax assets	133.0
Sweden subsidiaries
Income taxes
Net deferred tax assets	182.7
Swedish Tax Authority | Sweden subsidiaries
Uncertain tax positions
Reserve attributable to uncertain tax positions	$ 42.0