Discontinued Operations (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Pre Tax Gains And Losses For Energy Commodity Derivatives Designated As Cash Flow Hedges [Abstract]
Net gain (loss) recognized in other comprehensive income (loss) (effective portion)	$ (18)	$ (12)
Net gain (loss) reclassified from accumulated other comprehensive income (loss) into income (effective portion)	(18)	(13)
Gain (loss) recognized in income (ineffective portion)	0	0
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	38	39
Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	266
Segment, Discontinued Operations [Member]
Pre Tax Gains And Losses For Energy Commodity Derivatives Designated As Cash Flow Hedges [Abstract]
Net gain (loss) recognized in other comprehensive income (loss) (effective portion)	413	507
Net gain (loss) reclassified from accumulated other comprehensive income (loss) into income (effective portion)	332	355
Gain (loss) recognized in income (ineffective portion)	0	9
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract
Net gain (loss)	30	19
Revenues [Member]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract
Net gain (loss)	(2)	(1)
Revenues [Member] | Segment, Discontinued Operations [Member]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract
Net gain (loss)	30	47
Costs and Operating Expenses [Member] | Segment, Discontinued Operations [Member]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract
Net gain (loss)	$ 0	$ 28