Derivative Instruments and Hedging Activities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Derivative Instruments With Credit Risk Related Contingent Features	$ 0
Fair Value Hedging [Member]
Derivative [Line Items]
Fair Value Hedges, Net	0	0
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 0	$ 0
Natural Gas [Member] | Derivative Purchases [Member] | Designated as Hedging Instrument [Member] | Physical [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	50,000