Derivatives (Additional Cash Collateral The Utility Would Be Required To Post If Its Credit Risk-Related Contingency Features Were Triggered) (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Derivatives in a liability position with credit risk-related contingencies that are not fully collateralized		$ (16)	$ (24)
Related derivatives in an asset position		3	19
Collateral posting in the normal course of business related to these derivatives		11	4
Net position of derivative contracts/additional collateral posting requirements	[1]	$ (2)	$ (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.