Bradley Agreement - Schedule of Deficiency Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Deficiency Payments [Roll Forward]
Balance at beginning of year	$ 3.9	$ 7.8	$ 9.9
Deficiency payments made	0.0	0.1	0.2
Deficiency repayment received	(3.8)	(4.0)	(2.3)
Balance at end of year	$ 0.1	$ 3.9	$ 7.8