Financial and Other Derivative Instruments (Fair Value of Derivative Instruments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	$ 693	$ 833
Derivative Liability, Gross	(787)	(936)
Natural Gas Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	254	396
Derivative Liability, Gross	(342)	(503)
Electricity Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	386	400
Derivative Liability, Gross	(394)	(398)
Other Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	52	37
Derivative Liability, Gross	(48)	(34)
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	693	833
Derivative Liability, Gross	(787)	(936)
Not Designated as Hedging Instrument [Member] | Foreign currency exchange contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	1	0
Derivative Liability, Gross	(3)	(1)
Not Designated as Hedging Instrument [Member] | Natural Gas Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	254	396
Derivative Liability, Gross	(342)	(503)
Not Designated as Hedging Instrument [Member] | Electricity Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	386	400
Derivative Liability, Gross	(394)	(398)
Not Designated as Hedging Instrument [Member] | Other Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	52	37
Derivative Liability, Gross	(48)	(34)
Current Derivative Asset [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	605	691
Current Derivative Liability [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross	(696)	(773)
Noncurrent Derivative Asset [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross	88	142
Noncurrent Derivative Liability [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross	$ (91)	$ (163)