Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) bbl in Millions, $ in Millions		1 Months Ended	6 Months Ended
		May 31, 2019 Contract	Jun. 30, 2019 USD ($) Contract bbl Bcf	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Gain on the sale of swaption | $			$ 9.8
Carrying amount of hedged asset | $			$ 16.2	$ 50.2
Forward Starting Swaps [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract		2
Life of associated future debt		30 years
Forward Starting Swaps A [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract			1
Notional Amount | $			$ 75.0
Average Rate Locked			2.39%
Forward Starting Swaps B [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract			1
Notional Amount | $			$ 75.0
Average Rate Locked			2.41%
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]
Derivative [Line Items]
Current Volume | Bcf	[1],[2]		25.9
Designated as Hedging Instrument [Member] | Natural gas processing: Forecasted sales of NGLs [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		4.2
Designated as Hedging Instrument [Member] | Octane enhancement: Forecasted purchases of NGLs [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		1.3
Designated as Hedging Instrument [Member] | Octane enhancement: Forecasted sales of octane enhancement products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		2.0
Designated as Hedging Instrument [Member] | Natural gas marketing: Forecasted purchases of natural gas for fuel [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume | Bcf	[1],[2]		3.7
Designated as Hedging Instrument [Member] | Natural gas marketing: Natural gas storage inventory management activities [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Current Volume | Bcf	[1],[2]		1.7
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		55.0
Long Term Volume	[1],[2]		2.8
Designated as Hedging Instrument [Member] | NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		72.1
Long Term Volume	[1],[2]		0.8
Designated as Hedging Instrument [Member] | NGL marketing: NGLs inventory management activities [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		0.6
Designated as Hedging Instrument [Member] | Refined products marketing: Refined products inventory management activities [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		0.1
Designated as Hedging Instrument [Member] | Crude oil marketing: Forecasted purchases of crude oil [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		19.2
Designated as Hedging Instrument [Member] | Crude oil marketing: Forecasted sales of crude oil [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		26.2
Designated as Hedging Instrument [Member] | Propylene marketing: Forecasted sales of NGLs for propylene marketing activities [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		0.3
Not Designated as Hedging Instrument [Member] | Natural gas risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Current Volume | Bcf	[1],[2],[3]		47.5
Long Term Volume | Bcf	[1],[2],[3]		0.1
Not Designated as Hedging Instrument [Member] | Refined products risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2],[3]		1.8
Not Designated as Hedging Instrument [Member] | NGL risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2],[3]		5.4
Not Designated as Hedging Instrument [Member] | Crude oil risk management activities [Member] | Derivatives in mark-to-market relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2],[3]		39.0
Long Term Volume	[1],[2],[3]		1.6

[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 December 2020, December 2019 and December 2020, 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 transportation, processing and storage assets.