Asset Impairment and Sales (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Asset Impairments And Sales [Abstract]
Asset impairments and sales	$ (14)	$ (2)	$ (24)	$ (2)

The aggregate impact on earnings in the period of (a) the loss (gain) from the difference between the sale price or salvage price and the book value of an asset that was sold or retired during the reporting period, and (b) the charge against earnings resulting from the aggregate write down of all assets from their carrying value to their fair value.

No definition available.

Name:	us-gaap_LossesGainsOnSalesOfAssetsAndAssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration