Derivative Instruments, Hedging Activities and Fair Value Measurements, Gains and Losses on Derivative Instruments and Related Hedged Items (Details) (USD $) In Millions, unless otherwise specified									3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2012 Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2012 Commodity derivatives [Member]	Sep. 30, 2012 Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2012 Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2012 Derivatives in fair value hedging relationships [Member]	Sep. 30, 2011 Derivatives in fair value hedging relationships [Member]	Sep. 30, 2012 Derivatives in fair value hedging relationships [Member]	Sep. 30, 2011 Derivatives in fair value hedging relationships [Member]	Sep. 30, 2012 Derivatives in fair value hedging relationships [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2011 Derivatives in fair value hedging relationships [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2012 Derivatives in fair value hedging relationships [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2011 Derivatives in fair value hedging relationships [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2012 Derivatives in fair value hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2011 Derivatives in fair value hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2012 Derivatives in fair value hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2011 Derivatives in fair value hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member] Interest rate derivatives [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member] Interest rate derivatives [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member] Interest rate derivatives [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member] Interest rate derivatives [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2012 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2011 Derivatives in cash flow hedging relationships [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Aug. 31, 2012 Derivatives in cash flow hedging relationships [Member] Forward Starting Swaps [Member]	Feb. 29, 2012 Derivatives in cash flow hedging relationships [Member] Forward Starting Swaps [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Interest rate derivatives [Member] Location - Interest expense [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Revenue [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Commodity derivatives [Member] Location - Operating costs and expenses [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Foreign currency derivatives [Member] Location - Other income [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Foreign currency derivatives [Member] Location - Other income [Member]	Sep. 30, 2012 Derivatives not designated as hedging instruments [Member] Foreign currency derivatives [Member] Location - Other income [Member]	Sep. 30, 2011 Derivatives not designated as hedging instruments [Member] Foreign currency derivatives [Member] Location - Other income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(Loss) Recognized in Income on Derivative									$ 2.6	$ 32.2	$ (10.0)	$ 39.7	$ 3.0	$ 23.6	$ 6.1	$ 32.4	$ (0.4)	$ 8.6	$ (16.1)	$ 7.3																			$ (6.1)	$ (4.3)	$ 17.9	$ (1.5)	$ (2.2)	$ (8.8)	$ (5.5)	$ (19.3)	$ (3.9)	$ 4.3	$ 26.2	$ 17.6	$ 0	$ 0	$ (2.8)	$ 0	$ 0	$ 0.2	$ 0	$ 0.2
Gain/(Loss) Recognized in Income on Hedged Item									(4.7)	(30.2)	8.2	(41.0)	(2.9)	(22.5)	(6.3)	(32.2)	(1.8)	(7.7)	14.5	(8.8)
Change in Value Recognized in Other Comprehensive Income/(Loss) on Derivative (Effective Portion)																					(78.7)	(266.2)	(88.4)	(485.3)	(20.2)	(260.1)	(75.3)	(306.1)	(59.5)	8.8	0.7	(166.0)	1.0	(14.9)	(13.8)	(13.2)
Gain/(Loss) Reclassified from Accumulated Other Comprehensive Income/(Loss) to Income (Effective Portion)																					(5.4)	(36.7)	(48.0)	(183.4)	(4.5)	(1.6)	(10.9)	(4.6)	0.3	(33.2)	(12.3)	(181.7)	(1.2)	(1.9)	(24.8)	2.9
Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion)																					(1.0)	(0.9)	0.2	(0.7)					(1.1)	0	(0.2)	0.2	0.1	(0.9)	0.4	(0.9)
Accumulated other comprehensive loss related to interest rate derivative instruments expected to be reclassified to earnings in interest expense over the next twelve months					(30)
Accumulated other comprehensive income (loss) related to commodity derivative instruments expected to be reclassified to earnings over the next twelve months						0.9	0.1	0.8
Accumulated other comprehensive income (loss) related to interest rate derivative instruments	$ (393.4)	[1]	$ (329.0)	[1]																																	$ (70.2)	$ (115.3)

[1] See Note 4 for additional information regarding our derivative instruments.