Income Taxes, Reconciliation of the Benefit From (Provision For) Income Taxes (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of the benefit from (provision for) income taxes [Abstract]
Pre-Tax Net Book Income ("NBI")		$ 4,825.3	$ 3,761.4	$ 4,732.7
Texas Margin Tax	[1]	(41.9)	(32.1)	(44.2)
State income tax benefit (provision), net of federal benefit	[2]	(1.3)	9.2	(0.5)
Federal income tax benefit (provision) computed by applying the federal statutory rate to NBI of corporate entities		(13.1)	80.1	(0.9)
Federal benefit attributable to settlement of Liquidity Option Agreement	[2]	0.0	67.8	0.0
Valuation allowance	[3]	(14.2)	0.0	0.0
Other		0.5	(0.7)	0.0
Total benefit from (provision for) income taxes		$ (70.0)	$ 124.3	$ (45.6)
Effective income tax rate		(1.50%)	3.30%	(1.00%)

[1] Although the Texas Margin Tax is not considered a state income tax, it has the characteristics of an income tax since it is determined by applying a tax rate to a base that considers our Texas-sourced revenues and expenses.

[2] The total benefit recognized in income tax expense on March 5, 2020 from settlement of the Liquidity Option was $72.2 million, which is comprised of $4.4 million of state income tax benefit and $67.8 million of federal income tax benefit.

[3] Management believes that it is more likely than not that the net deferred tax assets attributable to OTA will not be fully realizable; therefore, we have provided for a valuation allowance.