Provision for Income Taxes (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Provision for Income Taxes [Abstract]
Maximum percent of qualifying income for publicly traded partnerships to be treated as corporations		90.00%
Current portion of income tax provision (benefit):
Federal		$ (1.3)	$ 5.3	$ 0.1
State		25.7	33.1	18.5
Foreign		1.2	0.5	1.0
Total current portion		25.6	38.9	19.6
Deferred portion of income tax provision (benefit):
Federal		1.6	(0.3)	(1.8)
State		18.5	21.7	7.9
Foreign		(0.1)	0.0	0.0
Total deferred portion		20.0	21.4	6.1
Total provision for income taxes		45.6	60.3	25.7
Reconciliation of the provision for (benefit from) income taxes [Abstract]
Pre-Tax Net Book Income ("NBI")		4,732.7	4,298.8	2,881.3
Texas Margin Tax	[1]	44.2	54.8	26.4
State income taxes (net of federal benefit)		0.5	0.2	0.5
Federal income taxes computed by applying the federal statutory rate to NBI of corporate entities		0.9	2.1	0.1
Other permanent differences		0.0	3.2	(1.3)
Total provision for income taxes		$ 45.6	$ 60.3	$ 25.7
Effective income tax rate		1.00%	1.40%	0.90%
Deferred tax liabilities:
Attributable to property, plant and equipment		$ 100.2	$ 80.8
Attributable to investments in partnerships		3.3	2.3
Total deferred tax liabilities		103.5	83.1
Less: Deferred tax assets:
Net operating loss carryovers	[2]	0.1	0.1
Temporary differences related to Texas Margin Tax		3.0	2.6
Total deferred tax assets		3.1	2.7
Total net deferred tax liabilities		$ 100.4	$ 80.4

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