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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis
Beginning Balance	$ 7	$ 2	$ 3	$ 1
Recorded in regulatory assets/liabilities	(3)	3	9	7
Purchases issuances and settlements [Abstract]
Settlements	0	0	(8)	(3)
Ending Balance	4	5	4	5
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) included in regulatory assets and liabilities	$ (1)	$ 3	$ 4	$ 5