Income Taxes - Unrecognized Tax Benefits (Details 7) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Uncertainties [Abstract]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 0.0
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	87.2	$ 89.4	$ 124.2
Decreases for prior year tax positions	(12.2)	(2.2)	(0.5)
Increases (decreases) for current year tax positions	0.3	0.0	0.3
Increases (decreases) related to tax rate changes (a)	0.0	0.0	(34.6)	[1]
Balance at end of year	75.3	87.2	$ 89.4
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	72.3	72.8
Unrecognized tax benefits that would result in adjustments to other tax accounts	$ 3.0	$ 14.5

[1] (a) As a result of the Tax Act, the value of unrecognized tax benefits associated with net operating loss carryforwards and other temporary differences was reduced to reflect the lower tax rates that will apply if the uncertainties related to these deferred tax assets materialize in the future.