Income Taxes - Schedule of components of income tax expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 223.7	$ 560.3	$ 787.0
State	4.8	(4.1)	8.8
Foreign	20.6	4.8	(1.4)
Total current tax expense	249.1	561.0	794.4
Deferred:
Federal	687.6	317.1	(377.4)
State	(1.9)	(1.3)	13.4
Foreign	(825.7)	3.2	3.9
Total deferred tax (benefit) expense	(140.0)	319.0	(360.1)
Total income tax expense (benefit)	$ 109.1	$ 880.0	$ 434.3