Income Taxes, Benefit From (Provision For) Income Taxes (Details) - USD ($) $ in Millions		10 Months Ended	12 Months Ended
	Mar. 05, 2020	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current portion of income tax benefit (provision):
Federal			$ 2.9	$ 1.3	$ (5.3)
State			(25.6)	(25.7)	(33.1)
Foreign			(0.6)	(1.2)	(0.5)
Total current portion			(23.3)	(25.6)	(38.9)
Deferred portion of income tax benefit (provision):
Federal			142.0	(1.6)	0.3
State			5.6	(18.5)	(21.7)
Foreign			0.0	0.1	0.0
Total deferred portion			147.6	(20.0)	(21.4)
Total benefit from (provision for) income taxes			124.3	(45.6)	(60.3)
OTA Holdings, Inc. [Member]
Deferred portion of income tax benefit (provision):
Federal	$ 67.8
State	4.4
Total benefit from (provision for) income taxes	$ 72.2	$ 83.1	$ 155.3	$ 0.0	$ 0.0