Hedging Activities and Fair Value Measurements (Details) bbl in Millions, $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) TWh bbl Bcf	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Derivative [Line Items]
Proceeds from (payments for) the settlement of interest rate derivative instruments | $				$ 75.2	$ (33.3)
Accumulated other comprehensive income | $		$ (198.7)	$ (147.1)	(198.7)	(147.1)	$ 71.4		$ (165.2)
Carrying amount of hedged asset | $		211.5		211.5				$ 144.0
Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Gain reclassified from accumulated other comprehensive income (loss) to income | $		$ 89.2	$ 199.0	(535.5)	$ 345.0
Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Mark-to-market loss in interest expense | $						$ (47.6)
Forward Starting Swaps A [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Notional amount of settled derivative instruments | $				675.0
Proceeds from (payments for) the settlement of interest rate derivative instruments | $				(0.1)
Gain reclassified from accumulated other comprehensive income (loss) to income | $				1.6
Cumulative gains on forward-starting swaps recognized in accumulated other comprehensive income | $							$ 47.5
Accumulated other comprehensive income | $							$ 45.9
Forward Starting Swaps B [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Notional amount of settled derivative instruments | $				400.0
Proceeds from (payments for) the settlement of interest rate derivative instruments | $				$ 75.3
Designated as Hedging Instrument [Member] | Natural gas processing: Forecasted natural gas purchases for plant thermal reduction (PTR) [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume | Bcf	[1],[2]			8.9
Designated as Hedging Instrument [Member] | Octane enhancement: Forecasted sales of octane enhancement products [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			9.2
Designated as Hedging Instrument [Member] | Octane enhancement: Forecasted sales of octane enhancement products [Member] | Derivatives in cash flow hedging relationships [Member] | Long-term [Member]
Derivative [Line Items]
Volume	[1],[2]			2.5
Designated as Hedging Instrument [Member] | Natural gas marketing: Natural gas storage inventory management activities [Member] | Derivatives in fair value hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume | Bcf	[1],[2]			3.4
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			120.7
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member] | Long-term [Member]
Derivative [Line Items]
Volume	[1],[2]			2.6
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			131.2
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member] | Long-term [Member]
Derivative [Line Items]
Volume	[1],[2]			3.0
Designated as Hedging Instrument [Member] | NGL marketing: NGLs inventory management activities [Member] | Derivatives in fair value hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			1.9
Designated as Hedging Instrument [Member] | Refined products marketing: Forecasted purchases of refined products [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			19.2
Designated as Hedging Instrument [Member] | Refined products marketing: Forecasted sales of refined products [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			28.2
Designated as Hedging Instrument [Member] | Refined products marketing: Refined products inventory management activities [Member] | Derivatives in fair value hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			0.8
Designated as Hedging Instrument [Member] | Crude oil marketing: Forecasted purchases of crude oil [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			12.2
Designated as Hedging Instrument [Member] | Crude oil marketing: Forecasted sales of crude oil [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			16.0
Designated as Hedging Instrument [Member] | Petrochemical marketing: Forecasted purchases of petrochemical products [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			0.9
Designated as Hedging Instrument [Member] | Petrochemical marketing: Forecasted sales of petrochemical products [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2]			1.2
Designated as Hedging Instrument [Member] | Commercial energy: Forecasted purchases of power related to asset operations [Member] | Derivatives in cash flow hedging relationships [Member] | Current [Member]
Derivative [Line Items]
Volume | TWh	[1],[2]			0.1
Designated as Hedging Instrument [Member] | Commercial energy: Forecasted purchases of power related to asset operations [Member] | Derivatives in cash flow hedging relationships [Member] | Long-term [Member]
Derivative [Line Items]
Volume | TWh	[1],[2]			0.1
Not Designated as Hedging Instrument [Member] | Natural gas risk management activities [Member] | Derivatives in mark-to-market relationships [Member] | Current [Member]
Derivative [Line Items]
Volume | Bcf	[1],[2],[3]			10.0
Not Designated as Hedging Instrument [Member] | Natural gas risk management activities [Member] | Derivatives in mark-to-market relationships [Member] | Long-term [Member]
Derivative [Line Items]
Volume | Bcf	[1],[2],[3]			0.3
Not Designated as Hedging Instrument [Member] | Refined products risk management activities [Member] | Derivatives in mark-to-market relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2],[3]			8.6
Not Designated as Hedging Instrument [Member] | NGL risk management activities [Member] | Derivatives in mark-to-market relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2],[3]			36.1
Not Designated as Hedging Instrument [Member] | NGL risk management activities [Member] | Derivatives in mark-to-market relationships [Member] | Long-term [Member]
Derivative [Line Items]
Volume	[1],[2],[3]			20.4
Not Designated as Hedging Instrument [Member] | Crude oil risk management activities [Member] | Derivatives in mark-to-market relationships [Member] | Current [Member]
Derivative [Line Items]
Volume	[1],[2],[3]			31.9
Not Designated as Hedging Instrument [Member] | Crude oil risk management activities [Member] | Derivatives in mark-to-market relationships [Member] | Long-term [Member]
Derivative [Line Items]
Volume	[1],[2],[3]			3.0

[1] The maximum term for derivatives designated as cash flow hedges, derivatives designated as fair value hedges and derivatives not designated as hedging instruments is February 2023, September 2021 and December 2023, respectively.

[2] Volume for derivatives designated as hedging instruments reflects the total amount of volumes hedged whereas volume for derivatives not designated as hedging instruments reflects the absolute value of derivative notional volumes.

[3] Reflects the use of derivative instruments to manage risks associated with our transportation, processing and storage assets.