Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 154.8	$ 213.6	$ 245.3
Other comprehensive income (loss), net of tax
Initial fair value	(0.1)	0.0	0.0
Realized gain (loss)	0.2	0.0	0.0
Unrealized gain (loss)	1.0	0.0	0.0
Reclassified to interest expense	(0.2)	0.0	0.0
Total	0.9	0.0	0.0
Deferred income tax expense	0.2	0.0	0.0
Other comprehensive income (loss)	0.7	0.0	0.0
Comprehensive income (loss)	$ 155.5	$ 213.6	$ 245.3