Significant Accounting Policies (Details 1) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	$ 177	$ 189
Less: Accumulated Amortization	41	34
Intangible Assets, Net	136	155
Less current intangible assets	14	20
Finite-Lived Intangible Assets, Net	122	135
Emission Allowances [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	3	6
Renewable Energy Credits [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	48	44
Contractual Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	$ 126	$ 139