Derivative Instruments, Hedging Activities and Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended				1 Months Ended
	Dec. 31, 2014		Dec. 31, 2013 Contract	Dec. 31, 2012 Contract	Oct. 31, 2014 Contract	Jul. 31, 2014 Contract	Oct. 14, 2014
Minimum [Member]
Derivative [Line Items]
Expected offset percentage of change in fair value derivative instrument (in hundredths)	80.00%
Maximum [Member]
Derivative [Line Items]
Expected offset percentage of change in fair value derivative instrument (in hundredths)	125.00%
Interest rate derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Forward Starting Swaps [Member]
Derivative [Line Items]
Number of derivative instruments settled			16	17
Notional amount of settled derivative instruments			$ 1,000.0	$ 850.0
Accumulated other comprehensive income (loss) related to interest rate derivative instruments			(168.8)	(185.5)
Interest rate derivatives [Member] | Derivatives in fair value hedging relationships [Member]
Derivative [Line Items]
Loss (gain) recognized due to settlement of derivative instruments							(27.6)
Interest rate derivatives [Member] | Derivatives in fair value hedging relationships [Member] | Senior Notes AA [Member]
Derivative [Line Items]
Number of derivative instruments settled					10
Notional amount of settled derivative instruments					750.0
Loss (gain) recognized due to settlement of derivative instruments							(17.6)
Interest rate derivatives [Member] | Derivatives in fair value hedging relationships [Member] | Senior Notes LL [Member]
Derivative [Line Items]
Number of derivative instruments settled					16
Notional amount of settled derivative instruments					800.0
Loss (gain) recognized due to settlement of derivative instruments							(10.0)
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				800.0
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 derivative instruments settled						6
Notional amount of settled derivative instruments						$ 600.0
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Natural gas processing: Forecasted sales of NGLs [Member]
Derivative [Line Items]
Current Volume	900,000	[1],[2],[3]
Forecasted NGL sales designated as normal sales agreements	100,000
Commodity derivatives [Member] | Derivatives in cash flow hedging relationships [Member] | Natural gas marketing: Forecasted sales of natural gas [Member]
Derivative [Line Items]
Current Volume	1,000,000,000	[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	9,900,000	[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	10,200,000	[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	1,200,000	[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	1,800,000	[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	5,800,000	[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	6,900,000	[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	8,600,000,000	[1],[2]
Commodity derivatives [Member] | Derivatives in fair value hedging relationships [Member] | Refined products marketing: Refined products inventory management activities [Member]
Derivative [Line Items]
Current Volume	200,000	[1],[2]
Commodity derivatives [Member] | Derivatives in mark-to-market relationships [Member] | Natural gas risk management activities [Member]
Derivative [Line Items]
Current Volume	81,400,000,000	[1],[2],[4],[5]
Long Term Volume	11,800,000,000	[1],[2],[4],[5]
Current natural gas hedging volumes designated as an index plus or minus a discount	35,200,000,000
Commodity derivatives [Member] | Derivatives in mark-to-market relationships [Member] | Crude oil risk management activities [Member]
Derivative [Line Items]
Current Volume	4,200,000	[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 December 2015, October 2015 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 0.1 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 35.2 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.