Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	$ 5	$ 6
Variable Interest Entity, Cash and cash equivalents	0	1
Variable Interest Entity, Electric utility plant, net	$ 5	$ 5

The net carrying amount of the consolidated Variable Interest Entity's assets and liabilities included in the reporting entity's statement of financial position.

No definition available.

Name:	us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant