Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Derivative [Line Items]
Accumulated other comprehensive income (loss) related to interest rate derivative instruments	$ (383.0)	[1]	$ (329.0)	[1]
Senior Notes AA [Member]
Derivative [Line Items]
Number of Derivatives Outstanding	10
Type of Derivatives Outstanding	fixed-to-floating swaps
Notional Amount	750.0
Period of Hedge	1/2011 to 2/2016
Rate Swap, fixed rate (in hundredths)	3.20%
Rate Swap, floating rate (in hundredths)	1.30%
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	600.0
Period of Hedge	5/2010 to 7/2014
Rate Swap, fixed rate (in hundredths)	2.00%
Rate Swap, floating rate (in hundredths)	0.40%
Accounting Treatment	Mark-to-market
Future Debt Offering Tranche Three [Member]
Derivative [Line Items]
Number of Derivatives Outstanding	16
Type of Derivatives Outstanding	forward starting swaps
Notional Amount	1,000.0
Expected Termination Date	3/2013
Average Rate Locked (in hundredths)	3.70%
Accounting Treatment	Cash flow hedge
Octane enhancement: Forecasted purchases of NGLs [Member]
Derivative [Line Items]
Current Volume	1.3	[2],[3]
Accounting Treatment	Cash flow hedge
Octane enhancement: Forecasted sales of octane enhancement products [Member]
Derivative [Line Items]
Current Volume	2.8	[2],[3]
Long Term Volume	0.1	[2],[3]
Accounting Treatment	Cash flow hedge
Natural gas marketing: Forecasted sales of natural gas [Member]
Derivative [Line Items]
Current Volume	3,200,000,000.0	[2],[3]
Accounting Treatment	Cash flow hedge
Natural gas marketing: Natural gas storage inventory management activities [Member]
Derivative [Line Items]
Current Volume	16,200,000,000.0	[2],[3]
Accounting Treatment	Fair value hedge
NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume	2.6	[2],[3]
Accounting Treatment	Cash flow hedge
NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume	5.5	[2],[3]
Accounting Treatment	Cash flow hedge
Refined products marketing: Forecasted purchases of refined products [Member]
Derivative [Line Items]
Current Volume	0.8	[2],[3]
Accounting Treatment	Cash flow hedge
Refined products marketing: Forecasted sales of refined products [Member]
Derivative [Line Items]
Current Volume	1.3	[2],[3]
Accounting Treatment	Cash flow hedge
Refined products marketing: Refined products inventory management activities [Member]
Derivative [Line Items]
Current Volume	0.1	[2],[3]
Accounting Treatment	Fair value hedge
Crude oil marketing: Forecasted purchases of crude oil [Member]
Derivative [Line Items]
Current Volume	3.1	[2],[3]
Accounting Treatment	Cash flow hedge
Crude oil marketing: Forecasted sales of crude oil [Member]
Derivative [Line Items]
Current Volume	6.2	[2],[3]
Accounting Treatment	Cash flow hedge
Natural gas risk management activities [Member]
Derivative [Line Items]
Current Volume	138,600,000,000.0	[2],[3],[4],[5]
Long Term Volume	24,700,000,000.0	[2],[3],[4],[5]
Accounting Treatment	Mark-to-market
Current natural gas hedging volumes designated as an index plus or minus a discount	39,300,000,000	[5]
Refined products risk management activities [Member]
Derivative [Line Items]
Current Volume	0.8	[2],[3],[4]
Accounting Treatment	Mark-to-market
Crude oil risk management activities [Member]
Derivative [Line Items]
Current Volume	3.9	[2],[3],[4]
Accounting Treatment	Mark-to-market
Derivatives in cash flow hedging relationships [Member] | Forward Starting Swaps [Member]
Derivative [Line Items]
Number of derivative instruments settled	17		3		1
Notional amount of settled derivative instruments	850.0		250.0		50.0
Accumulated other comprehensive income (loss) related to interest rate derivative instruments	(185.5)		(5.8)		1.3
Derivatives in cash flow hedging relationships [Member] | Treasury Rate Locks [Member]
Derivative [Line Items]
Number of derivative instruments settled			2
Notional amount of settled derivative instruments			1,230.0
Accumulated other comprehensive income (loss) related to interest rate derivative instruments			(17.4)
Derivatives in fair value hedging relationships [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Number of derivative instruments settled	11
Notional amount of settled derivative instruments	800.0
Loss (gain) recognized due to settlement of derivative instruments	$ (37.7)

[1] See Note 6 for additional information regarding our derivative instruments.

[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] The maximum term for derivatives designated as cash flow hedges, derivatives designated as fair value hedges and derivatives not designated as hedging instruments is January 2014, October 2013 and October 2015, respectively.

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

[5] Current volumes include 39.3 Bcf of physical derivative instruments that are predominantly priced at an index plus a premium or minus a discount related to location differences.