Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Segment Financial Information
External revenues	$ 3,729		$ 3,988
Internal revenues	0		2
Total revenues	3,729	[1]	3,990	[1]
Depreciation and amortization	353		354
Investment income	18		11
Interest expense	256		246
Income taxes	116		222
Net income (loss)	196		306
Total assets	50,424		47,691		50,406
Total goodwill	6,447		6,444		6,447
Property additions	826		517
Regulated Distribution
Segment Financial Information
External revenues	2,212		2,354
Internal revenues	0		0
Total revenues	2,212		2,354
Depreciation and amortization	202		216
Investment income	18		23
Interest expense	135		134
Income taxes	126		93
Net income (loss)	210		159
Total assets	26,943		25,595
Total goodwill	5,025		5,025
Property additions	436		266
Regulated Transmission
Segment Financial Information
External revenues	176		186
Internal revenues	0		0
Total revenues	176		186
Depreciation and amortization	29		30
Investment income	0		0
Interest expense	23		23
Income taxes	31		36
Net income (loss)	51		58
Total assets	4,722		4,408
Total goodwill	526		526
Property additions	89		63
Competitive Energy Services
Segment Financial Information
External revenues	1,414		1,519
Internal revenues	216		268
Total revenues	1,630		1,787
Depreciation and amortization	111		100
Investment income	16		6
Interest expense	71		65
Income taxes	(23)		83
Net income (loss)	(38)		141
Total assets	18,328		17,187
Total goodwill	896		893
Property additions	283		171
Other/Corporate
Segment Financial Information
External revenues	(27)		(24)
Internal revenues	0		0
Total revenues	(27)		(24)
Depreciation and amortization	11		8
Investment income	1		0
Interest expense	27		24
Income taxes	(18)		(16)
Net income (loss)	(30)		(28)
Total assets	431		501
Total goodwill	0		0
Property additions	18		17
Reconciling Adjustments
Segment Financial Information
External revenues	(46)		(47)
Internal revenues	(216)		(266)
Total revenues	(262)		(313)
Depreciation and amortization	0		0
Investment income	(17)		(18)
Interest expense	0		0
Income taxes	0		26
Net income (loss)	3		(24)
Total assets	0		0
Total goodwill	0		0
Property additions	$ 0		$ 0

[1] Includes excise tax collections of $114 million and $121 million in the three months ended March 31, 2013 and 2012, respectively.