Derivatives (Additional Cash Collateral The Utility Would Be Required To Post If Its Credit Risk-Related Contingency Features Were Triggered) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Derivatives in a liability position with credit risk-related contingencies that are not fully collateralized	$ (22)		$ (79)
Related derivatives in an asset position	1		4
Collateral posting in the normal course of business related to these derivatives	8		65
Net position of derivative contracts/additional collateral posting requirements	$ (13)	[1]	$ (10)	[1]

[1] This calculation excludes the impact of closed but unpaid positions, as their settlement is not impacted by any of the Utility?s credit risk-related contingencies.