Fair Value (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis
Beginning Balance	$ 1	$ 0	$ 1	$ 1
Recorded in regulatory assets/liabilities	3	4	4	5
Purchases issuances and settlements [Abstract]
Settlements	(2)	(2)	(3)	(4)
Ending Balance	2	2	2	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	$ 2	$ 2	$ 2	$ 2