Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) bbl in Millions, $ in Millions		1 Months Ended	9 Months Ended
		Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) Contract bbl Bcf
Interest Rate Swaps Hedging Senior Notes OO [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract			10
Type of Derivatives Outstanding			fixed-to-floating swaps
Notional Amount | $			$ 750.0
Period of Hedge			5/2015 to 5/2018
Rate Swap, fixed rate			1.65%
Rate Swap, floating rate			1.27%
Forward Starting Swaps A [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract			4
Type of Derivatives Outstanding			forward starting swaps
Notional Amount | $			$ 250.0
Expected Termination Date			Sep. 01, 2017
Average Rate Locked			1.91%
Life of associated future debt (in years)			30 years
Forward Starting Swaps B [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Number of Derivatives Outstanding | Contract			4
Type of Derivatives Outstanding			forward starting swaps
Notional Amount | $			$ 275.0
Expected Termination Date			May 01, 2018
Average Rate Locked			2.02%
Life of associated future debt (in years)			30 years
Unrealized gain on cash flow hedging instruments | $		$ 6.1
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]		24.4
Long Term Volume | Bcf	[1],[2]		3.3
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]		12.1
Long Term Volume	[1],[2]		3.5
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]		1.4
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]		3.3
Long Term Volume | Bcf	[1],[2]		0.5
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]		8.2
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]		78.2
Long Term Volume	[1],[2]		2.3
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]		99.0
Long Term Volume	[1],[2]		7.0
Designated as Hedging Instrument [Member] | Refined products marketing: Forecasted purchases of refined products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		0.3
Designated as Hedging Instrument [Member] | Refined products marketing: Forecasted sales of refined products [Member] | Derivatives in cash flow hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		0.4
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]		2.1
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]		7.4
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]		11.5
Designated as Hedging Instrument [Member] | Crude oil marketing: Crude oil inventory management activities [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Current Volume	[1],[2]		0.2
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],[4]		98.2
Long Term Volume | Bcf	[1],[2],[3],[4]		20.9
Current natural gas hedging volumes designated as an index plus or minus a discount | Bcf			25.4
Long-term natural gas hedging volumes designated as an index plus or minus a discount | Bcf			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],[4]		7.2
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],[4]		28.5
Long Term Volume	[1],[2],[4]		0.9

[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 2017, June 2017 and March 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] Current and long-term volumes include 25.4 Bcf and 1.8 Bcf, respectively, of physical derivative instruments that are predominantly priced at a marked-based index plus a premium or minus a discount related to location differences.

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