Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended
	Feb. 29, 2012	Mar. 31, 2012		Mar. 31, 2011
Senior Notes AA [Member]
Derivative [Line Items]
Number of Derivatives Outstanding		10
Type of Derivatives Outstanding		fixed-to-floating swaps
Notional Amount		$ 750
Period of Hedge		1/11 to 2/16
Rate Swap, fixed rate (in hundredths)		3.20%
Rate Swap, floating rate (in hundredths)		1.50%
Accounting Treatment		Fair value hedge
Undesignated Swaps [Member]
Derivative [Line Items]
Number of Derivatives Outstanding		6
Type of Derivatives Outstanding		floating-to-fixed swaps
Notional Amount		600
Period of Hedge		5/10 to 7/14
Rate Swap, fixed rate (in hundredths)		2.00%
Rate Swap, floating rate (in hundredths)		0.60%
Accounting Treatment		Mark-to-market
Interest Rate Swap [Member]
Derivative [Line Items]
(Increase)/decrease in interest expense recorded due to interest rate swaps		2.8		9.7
Number of derivative instruments settled	11
Notional amount of settled derivative instruments	800
Gain (loss) recognized due to settlement of derivative instruments	37.7
Future Debt Offering Tranche One [Member]
Derivative [Line Items]
Number of Derivatives Outstanding		7
Type of Derivatives Outstanding		forward starting swaps
Notional Amount		350
Expected Termination Date		8/12
Average Rate Locked (in hundredths)		3.70%
Accounting Treatment		Cash flow hedge
Future Debt Offering Tranche Two [Member]
Derivative [Line Items]
Number of Derivatives Outstanding		16
Type of Derivatives Outstanding		forward starting swaps
Notional Amount		1,000
Expected Termination Date		3/13
Average Rate Locked (in hundredths)		3.70%
Accounting Treatment		Cash flow hedge
Forward Starting Swaps [Member]
Derivative [Line Items]
Number of derivative instruments settled	10
Notional amount of settled derivative instruments	500
Gain (loss) recognized due to settlement of derivative instruments	$ (115.3)
Natural gas processing: Forecasted natural gas purchases for plant thermal reduction (PTR) [Member]
Derivative [Line Items]
Current Volume		27.7	[1],[2],[3]
Accounting Treatment		Cash flow hedge	[3]
Natural gas processing: Forecasted sales of NGLs [Member]
Derivative [Line Items]
Current Volume		2.4	[1],[2],[4]
Accounting Treatment		Cash flow hedge	[4]
Forecasted NGL sales designated as normal sales agreements		4.9
Octane enhancement: Forecasted purchases of NGLs [Member]
Derivative [Line Items]
Current Volume		0.3	[1],[2]
Accounting Treatment		Cash flow hedge
Octane enhancement: Forecasted sales of octane enhancement products [Member]
Derivative [Line Items]
Current Volume		3.2	[1],[2]
Accounting Treatment		Cash flow hedge
Natural gas marketing: Natural gas storage inventory management activities [Member]
Derivative [Line Items]
Current Volume		10.5	[1],[2]
Accounting Treatment		Fair value hedge
NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume		3.7	[1],[2]
Accounting Treatment		Cash flow hedge
NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume		3.6	[1],[2]
Long Term Volume		0.2	[1],[2]
Accounting Treatment		Cash flow hedge
Refined products marketing: Forecasted purchases of refined products [Member]
Derivative [Line Items]
Current Volume		0.4	[1],[2]
Accounting Treatment		Cash flow hedge
Refined products marketing: Forecasted sales of refined products [Member]
Derivative [Line Items]
Current Volume		0.4	[1],[2]
Accounting Treatment		Cash flow hedge
Refined products marketing: Refined products inventory management activities [Member]
Derivative [Line Items]
Current Volume		0.1	[1],[2]
Accounting Treatment		Fair value hedge
Crude oil marketing: Forecasted purchases of crude oil [Member]
Derivative [Line Items]
Current Volume		1.6	[1],[2]
Accounting Treatment		Cash flow hedge
Crude oil marketing: Forecasted sales of crude oil [Member]
Derivative [Line Items]
Current Volume		2.6	[1],[2]
Accounting Treatment		Cash flow hedge
Natural gas risk management activities [Member]
Derivative [Line Items]
Current Volume		416.9	[1],[2],[5],[6]
Long Term Volume		69.6	[1],[2],[5],[6]
Accounting Treatment		Mark-to-market	[5],[6]
Current natural gas hedging volumes designated as an index plus or minus a discount		104.2
Refined products risk management activities [Member]
Derivative [Line Items]
Current Volume		0.4	[1],[2],[5]
Accounting Treatment		Mark-to-market	[5]
Crude oil risk management activities [Member]
Derivative [Line Items]
Current Volume		6.1	[1],[2],[5]
Accounting Treatment		Mark-to-market	[5]

[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 2013, May 2012 and October 2015, 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] PTR represents the British thermal unit ("Btu") equivalent of the NGLs extracted from natural gas by a processing plant, and includes the natural gas used as plant fuel to extract those liquids, plant flare and other shortages.

[4] Forecasted sales of NGL volumes under natural gas processing exclude 4.9 MMBbls of additional hedges executed under contracts that have been designated as normal sales agreements.

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

[6] Current volumes include approximately 104.2 Bcf of physical derivative instruments that are predominantly priced at an index plus a premium or minus a discount related to location differences.