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	Mar. 31, 2015		Dec. 31, 2014
Derivatives in a liability position with credit risk-related contingencies that are not fully collateralized	$ (2)		$ (47)
Collateral posting in the normal course of business related to these derivatives	0		44
Net position of derivative contracts/additional collateral posting requirements	$ (2)	[1]	$ (3)	[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.