Income taxes - Deferred tax asset, net of valuation allowance and Uncertain tax positions (Details) $ in Millions	Jun. 30, 2019 USD ($)
Income taxes
Net deferred tax liability, net of valuation allowance	$ 55.3
Other net deferred tax liabilities	1.7
Uncertain tax positions
Total reserve for unrecognized tax benefits	63.3
Reversal of reserves for unrecognized tax benefits on permanent differences and interest and penalties	63.2
Reversal of reserves for unrecognized tax benefits on temporary differences	0.1
U.S. subsidiaries
Income taxes
Net deferred tax assets	32.7
Luxembourg subsidiaries
Income taxes
Net deferred tax assets	130.5
United Kingdom subsidiaries
Income taxes
Net deferred tax assets	12.9
Sweden subsidiaries
Income taxes
Net deferred tax assets	229.7
Swedish Tax Authority | Sweden subsidiaries
Uncertain tax positions
Reserve attributable to uncertain tax positions	$ 60.4