Income Taxes - Schedule of components of income tax expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 199.0	$ 444.6	$ 223.7
State	1.2	1.9	4.8
Foreign	21.4	(2.6)	20.6
Total current tax expense	221.6	443.9	249.1
Deferred:
Federal	109.0	(132.0)	687.6
State	(2.0)	(1.7)	(1.9)
Foreign	(31.4)	3.1	(825.7)
Total deferred tax (benefit) expense	75.6	(130.6)	(140.0)
Total income tax expense (benefit)	$ 297.2	$ 313.3	$ 109.1