Fair Value Measurements (Schedule of Changes in Fair Value of the Level 3 Assets and Liabilities (All Related to Commodity Contracts)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013 Level 3 [Member] Commodity contracts [Member] Derivative financial instruments, assets and liabilities [Member]		Sep. 30, 2012 Level 3 [Member] Commodity contracts [Member] Derivative financial instruments, assets and liabilities [Member]		Sep. 30, 2013 Level 3 [Member] Commodity contracts [Member] Derivative financial instruments, assets and liabilities [Member]		Sep. 30, 2012 Level 3 [Member] Commodity contracts [Member] Derivative financial instruments, assets and liabilities [Member]		Sep. 30, 2013 Texas Competitive Electric Holdings Company LLC [Member] Interest rate swaps [Member]	Dec. 31, 2012 Texas Competitive Electric Holdings Company LLC [Member] Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Accumulated Unrealized Gain (Loss) On Interest Rate Derivative Instruments Not Designated As Hedging Instruments									$ 1,520	$ 2,065
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	88		12		29		53
Total unrealized valuation gains (losses)	(24)		12		(41)		(5)
Purchases, issuances and settlements:
Purchases	6	[1]	17	[1]	66	[1]	30	[1]
Issuances	0	[1]	(4)	[1]	(6)	[1]	(15)	[1]
Settlements	(62)	[1]	(56)	[1]	(45)	[1]	(34)	[1]
Transfers into Level 3	(1,179)	[2]	3	[2]	(1,178)	[2]	(42)	[2]
Transfers out of Level 3	0	[2]	0	[2]	4	[2]	(3)	[2]
Net change	(1,259)	[3]	(28)	[3]	(1,200)	[3]	(69)	[3]
Balance at end of period	(1,171)		(16)		(1,171)		(16)
Unrealized valuation gains (losses) relating to instruments held at end of period	254		15		280		(22)
Accumulated Unrealized Gain (Loss) On Interest Rate Derivative Instruments Not Designated As Hedging Instruments Net Of Nonperformance Risk Adjustments									$ 1,167

[1] Settlements reflect reversals of unrealized mark-to-market valuations previously recognized in net income. Purchases and issuances reflect option premiums paid or received.

[2]

[3] Substantially all changes in values of commodity contracts are reported in the income statement in net gain (loss) from commodity hedging and trading activities. Changes in values of interest rate swaps are reported in the income statement in interest expense and related charges. Activity excludes changes in fair value in the month the position settled as well as amounts related to positions entered into and settled in the same month.