Summary of Accounting Policies - Risk Management Activities (Details) (Forward Contracts, USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Forward Contracts
Derivative [Line Items]
Net asset position (less than $1 million dollars)	$ (1)

- Definition

Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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