Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) (Commodity derivatives [Member])	Mar. 31, 2015 ft3
Derivatives in cash flow hedging relationships [Member] | Natural gas processing: Forecasted natural gas purchases for plant thermal reduction (PTR) [Member]
Derivative [Line Items]
Current Volume	12,800,000,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | Natural gas processing: Forecasted sales of NGLs [Member]
Derivative [Line Items]
Current Volume	4,200,000	[1],[2],[3]
Forecasted NGL sales designated as normal sales agreements	1,300,000
Derivatives in cash flow hedging relationships [Member] | Natural gas marketing: Forecasted purchases of natural gas [Member]
Derivative [Line Items]
Current Volume	11,100,000,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | Natural gas marketing: Forecasted sales of natural gas [Member]
Derivative [Line Items]
Current Volume	2,100,000,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume	18,500,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume	18,600,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | Refined products marketing: Forecasted purchases of refined products [Member]
Derivative [Line Items]
Current Volume	1,200,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | Refined products marketing: Forecasted sales of refined products [Member]
Derivative [Line Items]
Current Volume	1,800,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | Crude oil marketing: Forecasted purchases of crude oil [Member]
Derivative [Line Items]
Current Volume	9,300,000	[1],[2]
Long Term Volume	400,000	[1],[2]
Derivatives in cash flow hedging relationships [Member] | Crude oil marketing: Forecasted sales of crude oil [Member]
Derivative [Line Items]
Current Volume	11,500,000	[1],[2]
Long Term Volume	400,000	[1],[2]
Derivatives in fair value hedging relationships [Member] | Natural gas marketing: Natural gas storage inventory management activities [Member]
Derivative [Line Items]
Current Volume	3,500,000,000	[1],[2]
Derivatives in fair value hedging relationships [Member] | Refined products marketing: Refined products inventory management activities [Member]
Derivative [Line Items]
Current Volume	1,100,000	[1],[2]
Derivatives in mark-to-market relationships [Member] | Natural gas risk management activities [Member]
Derivative [Line Items]
Current Volume	89,500,000,000	[1],[2],[4],[5]
Long Term Volume	10,000,000,000	[1],[2],[4],[5]
Current natural gas hedging volumes designated as an index plus or minus a discount	56,200,000,000
Derivatives in mark-to-market relationships [Member] | NGL risk management activities [Member]
Derivative [Line Items]
Current Volume	1,800,000	[1],[2],[4]
Derivatives in mark-to-market relationships [Member] | Crude oil risk management activities [Member]
Derivative [Line Items]
Current Volume	5,500,000	[1],[2],[4]

[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 June 2016, February 2016 and March 2018, 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] Forecasted sales of NGL volumes under natural gas processing exclude 1.3 MMBbls of additional hedges executed under contracts that have been designated as normal sales agreements.

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

[5] Current volumes include 56.2 Bcf of physical derivative instruments that are predominantly priced at a marked-based index plus a premium or minus a discount related to location differences.