Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Segment Financial Information
External revenues									$ 15,301		$ 16,080		$ 13,265
Internal revenues									2		67		74
Total revenues									15,303	[1]	16,147	[1]	13,339	[1]
Depreciation and amortization									1,056		1,395		1,472
Investment income									77		114		117
Net interest charges									(1,001)		(1,008)		(845)
Income taxes	(105)	309	127	222	24	325	114	111	553		574		462
NET INCOME	(148)	425	188	306	99	530	193	47	771		869		718
Total assets	50,406				47,326				50,406		47,326		35,531
Total goodwill	6,447				6,441				6,447		6,441		5,575
Property additions									2,678		2,129		1,780
Regulated Distribution
Segment Financial Information
External revenues									8,897		9,740		9,422
Internal revenues									0		0		139
Total revenues									8,897		9,740		9,561
Depreciation and amortization									493		846		1,094
Investment income									84		99		35
Net interest charges									(540)		(530)		(395)
Income taxes									295		287		307
NET INCOME									540		488		522
Total assets	27,150				25,534				27,150		25,534		20,340
Total goodwill	5,025				5,025				5,025		5,025		5,025
Property additions									1,074		868		490
Regulated Transmission
Segment Financial Information
External revenues									740		660		398
Internal revenues									0		0		0
Total revenues									740		660		398
Depreciation and amortization									115		110		80
Investment income									1		0		0
Net interest charges									(92)		(89)		(66)
Income taxes									133		114		50
NET INCOME									226		194		85
Total assets	4,777				4,379				4,777		4,379		2,884
Total goodwill	526				526				526		526		526
Property additions									507		390		255
Competitive Energy Services
Segment Financial Information
External revenues									5,808		5,825		3,575
Internal revenues									866		1,237		2,301
Total revenues									6,674		7,062		5,876
Depreciation and amortization									414		415		284
Investment income									66		56		51
Net interest charges									(284)		(298)		(232)
Income taxes									91		222		128
NET INCOME									215		377		210
Total assets	18,087				16,796				18,087		16,796		11,320
Total goodwill	896				890				896		890		24
Property additions									1,014		778		976
Other/Corporate
Segment Financial Information
External revenues									(119)		(114)		28
Internal revenues									0		0		0
Total revenues									(119)		(114)		28
Depreciation and amortization									34		24		14
Investment income									(5)		1		(2)
Net interest charges									(85)		(91)		(155)
Income taxes									(34)		(87)		(47)
NET INCOME									(155)		(149)		(79)
Total assets	392				617				392		617		987
Total goodwill	0				0				0		0		0
Property additions									83		93		59
Reconciling Adjustments
Segment Financial Information
External revenues									(25)		(31)		(158)
Internal revenues									(864)		(1,170)		(2,366)
Total revenues									(889)		(1,201)		(2,524)
Depreciation and amortization									0		0		0
Investment income									(69)		(42)		33
Net interest charges									0		0		3
Income taxes									68		38		24
NET INCOME									(55)		(41)		(20)
Total assets	0				0				0		0		0
Total goodwill	0				0				0		0		0
Property additions									$ 0		$ 0		$ 0

[1] Includes excise tax collections of $455 million, $486 million and $428 million in 2012, 2011 and 2010, respectively.