Goodwill and Other Intangible Assets (Intangible Assets Acquired) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Indefinite-lived Intangible Assets [Line Items]
Indefinite Lived Intangible Asset Acquired Amount	$ 19	$ 5
Renewable energy certificates
Indefinite-lived Intangible Assets [Line Items]
Indefinite Lived Intangible Asset Acquired Amount	3	3
Other
Indefinite-lived Intangible Assets [Line Items]
Indefinite Lived Intangible Asset Acquired Amount	$ 16	$ 2