Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Counterparty default risk liability valuation adjustment related to derivative contracts	$ 7	$ 4

Amount of credit risk valuation adjustment to derivative liabilities to properly reflect the credit quality of the entity.

No definition available.

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