Income Taxes - Schedule of components of income tax provision (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United States federal:
Current	$ 17.4	$ (3.2)	$ 1.4
Deferred	(14.6)	(47.8)	(180.4)
Total United States federal income taxes	2.8	(51.0)	(179.0)
United States state and local:
Current	13.4	(0.2)	17.1
Deferred	(19.5)	(1.1)	4.6
Total United States state and local income taxes	(6.1)	(1.3)	21.7
All other countries:
Current	57.9	37.1	44.4
Deferred	(12.0)	(9.8)	(7.6)
Total all other countries income taxes	45.9	27.3	36.8
Total income tax provision/(benefit)	$ 42.6	$ (25.0)	$ (120.5)