Income taxes - statements of operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income (loss) before income taxes:
United States	$ 618.0	$ 555.0	$ (2.6)
Foreign	233.1	198.0	64.9
Income before income taxes	851.1	753.0	62.3
Current income tax (expense) benefit
Federal	(119.9)	(74.0)	30.4
State	(32.2)	(32.3)	(4.8)
Foreign	(81.6)	(91.8)	(58.8)
Subtotal	(233.7)	(198.1)	(33.2)
Deferred income tax (expense) benefit
Federal	18.0	(11.6)	28.0
State	4.4	(1.9)	14.4
Foreign	46.7	31.2	45.1
Subtotal	69.1	17.7	87.5
Income tax (expense) benefit	$ (164.6)	$ (180.4)	$ 54.3