Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended			9 Months Ended
	Mar. 31, 2013 ContractINF	Aug. 31, 2012 ContractINF	Feb. 29, 2012 ContractINF	Sep. 30, 2013		Dec. 31, 2012 ContractINF
Interest rate derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Forward Starting Swaps [Member]
Derivative [Line Items]
Number of Derivatives Outstanding						16
Type of Derivatives Outstanding				forward starting interest rate swaps
Notional Amount						$ 1,000.0
Number of derivative instruments settled	16	7	10
Notional amount of settled derivative instruments	1,000	350	500
Accumulated other comprehensive income (loss) related to interest rate derivative instruments	(168.8)	(70.2)	(115.3)
Interest rate derivatives [Member] | Derivatives in fair value hedging relationships [Member] | 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)				1.20%
Interest rate derivatives [Member] | 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
Loss (gain) recognized due to settlement of derivative instruments			(37.7)
Interest rate derivatives [Member] | Derivatives in mark-to-market relationships [Member] | 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)				0.30%
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Natural gas processing: Forecasted sales of NGLs [Member]
Derivative [Line Items]
Current Volume				0.1	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Octane enhancement: Forecasted purchases of NGLs [Member]
Derivative [Line Items]
Current Volume				1.0	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Octane enhancement: Forecasted sales of octane enhancement products [Member]
Derivative [Line Items]
Current Volume				3.2	[1],[2]
Long Term Volume				0.7	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Natural gas marketing: Forecasted sales of natural gas [Member]
Derivative [Line Items]
Current Volume				2,400,000,000.0	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | NGL marketing: Forecasted purchases of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume				3.6	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | NGL marketing: Forecasted sales of NGLs and related hydrocarbon products [Member]
Derivative [Line Items]
Current Volume				7.3	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Refined products marketing: Forecasted purchases of refined products [Member]
Derivative [Line Items]
Current Volume				0.8	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Refined products marketing: Forecasted sales of refined products [Member]
Derivative [Line Items]
Current Volume				1.0	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Crude oil marketing: Forecasted purchases of crude oil [Member]
Derivative [Line Items]
Current Volume				3.7	[1],[2]
Long Term Volume				0.3	[1],[2]
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Crude oil marketing: Forecasted sales of crude oil [Member]
Derivative [Line Items]
Current Volume				5.1	[1],[2]
Long Term Volume				0.5	[1],[2]
Commodity derivatives [Member] | Derivatives in fair value hedging relationships [Member] | Natural gas marketing: Natural gas storage inventory management activities [Member]
Derivative [Line Items]
Current Volume				10,000,000,000.0	[1],[2]
Commodity derivatives [Member] | Derivatives in mark-to-market relationships [Member] | Natural gas risk management activities [Member]
Derivative [Line Items]
Current Volume				112,200,000,000.0	[1],[2],[3],[4]
Long Term Volume				23,800,000,000.0	[1],[2],[3],[4]
Current natural gas hedging volumes designated as an index plus or minus a discount				52,000,000,000
Long-term natural gas hedging volumes designated as an index plus or minus a discount				300,000,000
Commodity derivatives [Member] | Derivatives in mark-to-market relationships [Member] | Refined products risk management activities [Member]
Derivative [Line Items]
Current Volume				0.6	[1],[2],[3]
Commodity derivatives [Member] | Derivatives in mark-to-market relationships [Member] | Crude oil risk management activities [Member]
Derivative [Line Items]
Current Volume				11.0	[1],[2],[3]
Long Term Volume				0.9	[1],[2],[3]

[1] 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.

[2] 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 2015, May 2014 and October 2016, respectively.

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

[4] Current and long-term volumes include 52.0 Bcf and 0.3 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.