Benefit Plans - Costs of Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Pension Benefits
Defined benefit plan disclosure
Service cost	$ 16		$ 14		$ 32		$ 27
Interest cost	33		35		67		70
Expected return on plan assets	(46)		(45)		(93)		(91)
Amortization of actuarial loss	26	[1]	18	[1]	48	[1]	33	[1]
Other amortization, net	2	[1]	1	[1]	4	[1]	3	[1]
Net periodic cost	31		23		58		42
Pension Benefits | PEC
Defined benefit plan disclosure
Service cost	7		6		13		11
Interest cost	15		16		29		31
Expected return on plan assets	(24)		(23)		(47)		(46)
Amortization of actuarial loss	10		7		20		13
Other amortization, net	2		1		4		3
Net periodic cost	10		7		19		12
Pension Benefits | PEF
Defined benefit plan disclosure
Service cost	7		6		14		12
Interest cost	15		15		29		30
Expected return on plan assets	(20)		(20)		(40)		(39)
Amortization of actuarial loss	12		9		23		17
Other amortization, net	0		0		0		0
Net periodic cost	14		10		26		20
Other Postretirement Benefits
Defined benefit plan disclosure
Service cost	4		3		7		6
Interest cost	11		10		21		20
Expected return on plan assets	0		0		(1)		(1)
Amortization of actuarial loss	9	[1]	3	[1]	15	[1]	6	[1]
Other amortization, net	1	[1]	1	[1]	2	[1]	3	[1]
Net periodic cost	25		17		44		34
Other Postretirement Benefits | PEC
Defined benefit plan disclosure
Service cost	2		2		4		2
Interest cost	6		5		11		10
Expected return on plan assets	0		0		0		0
Amortization of actuarial loss	6		1		8		2
Other amortization, net	0		0		0		1
Net periodic cost	14		8		23		15
Other Postretirement Benefits | PEF
Defined benefit plan disclosure
Service cost	1		1		3		2
Interest cost	4		4		9		9
Expected return on plan assets	0		0		(1)		(1)
Amortization of actuarial loss	3		2		5		4
Other amortization, net	1		1		2		2
Net periodic cost	$ 9		$ 8		$ 18		$ 16

[1] Adjusted to reflect PEF’s rate treatment. See Note 17B in the 2011 Form 10-K.