Fair Value (Reconciliation of Level 3 Assets and Liabilities at Fair Value on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis
Beginning Balance	$ 1	$ 1	$ 3	$ 1
Recorded in regulatory assets/liabilities	7	3	11	4
Purchases issuances and settlements [Abstract]
Settlements	(1)	(2)	(7)	(3)
Ending Balance	7	2	7	2
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) included in regulatory assets and liabilities	$ 7	$ 2	$ 7	$ 2