Income Taxes (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		7 Months Ended	9 Months Ended
		Mar. 05, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
OTA Deferred Tax Liability:
Liquidity Option liability		$ 511.9
Series A cumulative convertible preferred units (in dollars per unit)			$ 1,000		$ 1,000	$ 1,000
Current portion of income tax benefit (provision):
Federal			$ 5.3	$ 0.4		$ 3.0	$ (0.1)
State			(4.7)	(9.1)		(13.4)	(25.6)
Foreign			0.2	0.0		0.0	(0.8)
Total current portion			0.8	(8.7)		(10.4)	(26.5)
Deferred portion of income tax benefit (provision):
Federal		67.8	18.7	(0.3)		145.1	(0.2)
State		4.4	(0.4)	(6.4)		3.9	(10.9)
Foreign			0.0	0.0		0.0	0.2
Total deferred portion			18.3	(6.7)		149.0	(10.9)
Total benefit from (provision for) income taxes			19.1	$ (15.4)		138.6	$ (37.4)
Deferred tax liabilities:
Attributable to investment in OTA			353.9		$ 353.9	353.9
Attributable to property, plant and equipment			107.9		107.9	107.9		$ 100.2
Attributable to investments in other entities			4.2		4.2	4.2		3.3
Total deferred tax liabilities			466.0		466.0	466.0		103.5
Less: deferred tax assets:
Net operating loss carryovers	[1]		0.1		0.1	0.1		0.1
Temporary differences related to Texas Margin Tax			2.6		2.6	2.6		3.0
Total deferred tax assets			2.7		2.7	2.7		3.1
Total net deferred tax liabilities			463.3		463.3	463.3		$ 100.4
OTA Holdings, Inc. [Member]
Deferred portion of income tax benefit (provision):
Total benefit from (provision for) income taxes		72.2	$ 21.3		$ 85.8	$ 158.0
Deferred tax liabilities:
Total deferred tax liabilities		$ 439.7

[1] These losses expire in various years between 2020 and 2037 and are subject to limitations on their utilization.