Significant Accounting Policies (Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	$ 179	$ 179
Less: Accumulated Amortization	48	45
Intangible Assets, Net	131	134
Less current intangible assets	13	12
Finite-Lived Intangible Assets, Net	118	122
Emission Allowances [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	2	2
Renewable Energy Credits [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	50	51
Contract Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	$ 127	$ 126