Income Taxes (Details) - USD ($) $ in Millions			1 Months Ended	3 Months Ended
		Mar. 05, 2020	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
OTA Deferred Tax Liability:
Liquidity Option liability		$ 511.9
Current portion of income tax benefit (provision):
Federal				$ 0.8	$ (0.1)
State				(5.1)	(4.6)
Foreign				(1.1)	(0.2)
Total current portion				(5.4)	(4.9)
Deferred portion of income tax benefit (provision):
Federal		67.8		(5.9)	172.8
State		4.4		1.3	11.3
Total deferred portion				(4.6)	184.1
Total benefit from (provision for) income taxes				(10.0)	179.2
Deferred tax liabilities:
Attributable to investment in OTA				362.9		$ 356.6
Attributable to property, plant and equipment				105.2		106.4
Attributable to investments in other entities				4.0		4.1
Other				13.5		0.0
Total deferred tax liabilities				485.6		467.1
Less: deferred tax assets:
Net operating loss carryovers	[1]			2.9		0.1
Temporary differences related to Texas Margin Tax				2.7		2.3
Total deferred tax assets				5.6		2.4
Total net deferred tax liabilities before valuation allowance				480.0		464.7
Less: Valuation allowance on deferred tax assets				2.8		0.0
Total net deferred tax liabilities				482.8		$ 464.7
Net operating loss carryover subject to expiration				0.1
Net operating loss carryover not subject to expiration				2.8
OTA Holdings, Inc. [Member]
Deferred portion of income tax benefit (provision):
Total benefit from (provision for) income taxes		72.2	$ 115.0	$ (6.3)	$ 187.2
Deferred tax liabilities:
Total deferred tax liabilities		$ 439.7

[1] Of the loss amount presented for March 31, 2021, $0.1 million expires in various years between 2021 and 2037.  The remaining $2.8 million has an indefinite carryover period.  All losses are subject to limitations on their utilization.