Fair Value Measurements (Schedule of Changes in Fair Value of the Level 3 Assets and Liabilities (All Related to Commodity Contracts)) (Details) - Level 3 [Member] - Commodity contracts [Member] - Derivative financial instruments, assets and liabilities [Member] - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net asset (liability) balance at beginning of period		$ 44	$ 45	$ 35	$ (973)
Total unrealized valuation gains (losses)		(1)	(3)	13	(97)
Purchases, issuances and settlements:
Purchases	[1]	5	10	37	39
Issuances	[1]	(2)	(1)	(7)	(3)
Settlements	[1]	(19)	(21)	(44)	1,063
Transfers into Level 3	[2]	0	0	0	0
Transfers out of Level 3	[2]	0	(1)	(7)	0
Net change	[3]	(17)	(16)	(8)	1,002
Net asset balance at end of period		27	29	27	29
Unrealized valuation gains relating to instruments held at end of period		$ 1	$ 0	$ 1	$ 2

[1] Settlements reflect reversals of unrealized mark-to-market valuations previously recognized in net income. Purchases and issuances reflect option premiums paid or received. Settlement amounts in the nine months ended September 30, 2014 reflect termination of the TCEH interest rate swaps and include the reversal of a nonperformance risk adjustment as discussed in Note 13.

[2] Includes transfers due to changes in the observability of significant inputs. Transfers in and out occur at the end of each quarter, which is when the assessments are performed. All Level 3 transfers during the periods presented are in and out of Level 2.

[3] Substantially all changes in values of commodity contracts are reported in the condensed statements of consolidated income (loss) in net gain (loss) from commodity hedging and trading activities. Activity excludes changes in fair value in the month the positions settled as well as amounts related to positions entered into and settled in the same quarter.