Supplementary Financial Information - (Restricted Cash) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Current Assets	$ 364	$ 2
Noncurrent Assets	506	901
Other Restricted Cash [Member]
Current Assets	0	2
Noncurrent Assets	0	0
Texas Competitive Electric Holdings Company LLC | Amount Related To Texas Competitive Electric Company LLC Debtor-In-Possession Facility [Member]
Current Assets	364	0
Noncurrent Assets	0	350
Texas Competitive Electric Holdings Company LLC | Amount Related To Texas Competitive Electric Holdings Company LLC Letter Of Credit Facility [Member]
Current Assets	0	0
Noncurrent Assets	$ 506	$ 551