Risk Management and Hedging Activities Risk Management and Hedging Activities - Collateral and Contingent Features (Details) (Commodity Contract [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commodity Contract [Member]
Derivative [Line Items]
Derivative, Net Liability Position, Aggregate Fair Value	$ 22	$ 68
Collateral Already Posted, Aggregate Fair Value	0	12
Additional Collateral, Aggregate Fair Value	$ 13	$ 51