Benefit Plans - Costs of Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Pension Benefits [Member]
Defined benefit plan disclosure
Service cost	$ 16		$ 13		$ 47		$ 39
Interest cost on projected benefit obligation	32		33		95		98
Expected return on plan assets	(48)		(45)		(141)		(136)
Amortization of prior service cost (credit)	2	[1]	2	[1]	7	[1]	5	[1]
Amortization of net transition liability	0	[1]	0	[1]	0	[1]	0	[1]
Amortization of actuarial loss	24	[1]	15	[1]	69	[1]	47	[1]
Special termination costs	0		0		0		0
Other	1		0		1		0
Net periodic cost	27		18		78		53
Defined benefit plan, weighted average assumptions used in calculating net periodic benefit cost
Discount rate					4.60%
Rate of increase in future compensation
Bargaining					4.00%
Expected long-term rate of return on plan assets					8.00%
Pension Benefits [Member] | PEC [Member]
Defined benefit plan disclosure
Service cost	6		5		19		15
Interest cost on projected benefit obligation	15		15		43		46
Expected return on plan assets	(25)		(23)		(72)		(68)
Amortization of prior service cost (credit)	2		1		6		4
Amortization of net transition liability	0		0		0		0
Amortization of actuarial loss	9		7		28		19
Special termination costs	0		0		0		0
Other	1		0		1		0
Net periodic cost	8		5		25		16
Pension Benefits [Member] | PEF [Member]
Defined benefit plan disclosure
Service cost	8		6		22		18
Interest cost on projected benefit obligation	14		14		42		43
Expected return on plan assets	(21)		(19)		(61)		(59)
Amortization of net transition liability	0		0		0		0
Amortization of actuarial loss	13		8		36		25
Special termination costs	0		0		0		0
Net periodic cost	14		9		39		27
Nonqualified Pension Plans [Member]
Defined benefit plan disclosure
Service cost	0		0		1		1
Interest cost on projected benefit obligation	2		2		6		7
Expected return on plan assets	0		0		0		0
Amortization of prior service cost (credit)	0	[1]	0	[1]	0	[1]	0	[1]
Amortization of net transition liability	0	[1]	0	[1]	0	[1]	0	[1]
Amortization of actuarial loss	1	[1]	1	[1]	3	[1]	2	[1]
Special termination costs	0		0		0		0
Other	0		0		0		0
Net periodic cost	3		3		10		10
Defined benefit plan, weighted average assumptions used in calculating net periodic benefit cost
Discount rate					4.60%
Rate of increase in future compensation
Supplementary plans					5.25%
Nonqualified Pension Plans [Member] | PEC [Member]
Defined benefit plan disclosure
Service cost	0		0		1		1
Interest cost on projected benefit obligation	1		1		1		1
Expected return on plan assets	0		0		0		0
Amortization of prior service cost (credit)	0		0		0		0
Amortization of net transition liability	0		0		0		0
Amortization of actuarial loss	0		0		1		0
Special termination costs	0		0		0		0
Other	0		0		0		0
Net periodic cost	1		1		3		2
Nonqualified Pension Plans [Member] | PEF [Member]
Defined benefit plan disclosure
Service cost	0		0		0		0
Interest cost on projected benefit obligation	1		1		2		2
Expected return on plan assets	0		0		0		0
Amortization of net transition liability	0		0		0		0
Amortization of actuarial loss	0		0		0		0
Special termination costs	0		0		0		0
Net periodic cost	1		1		2		2
Other Postretirement Benefits [Member]
Defined benefit plan disclosure
Service cost	5		3		12		8
Interest cost on projected benefit obligation	11		10		32		30
Expected return on plan assets	0		0		(1)		(1)
Amortization of prior service cost (credit)	0	[1]	0	[1]	0	[1]	0	[1]
Amortization of net transition liability	1	[1]	1	[1]	3	[1]	4	[1]
Amortization of actuarial loss	10	[1]	3	[1]	25	[1]	9	[1]
Special termination costs	5		0		5		0
Other	0		0		0		0
Net periodic cost	32		17		76		50
Defined benefit plan, weighted average assumptions used in calculating net periodic benefit cost
Discount rate					4.60%
Other Postretirement Benefits [Member] | PEC [Member]
Defined benefit plan disclosure
Service cost	2		2		6		3
Interest cost on projected benefit obligation	6		5		17		15
Expected return on plan assets	0		0		0		0
Amortization of prior service cost (credit)	0		0		0		0
Amortization of net transition liability	0		0		0		1
Amortization of actuarial loss	6		1		14		4
Special termination costs	2		0		2		0
Other	0		0		0		0
Net periodic cost	16		8		39		23
Other Postretirement Benefits [Member] | PEF [Member]
Defined benefit plan disclosure
Service cost	2		1		5		3
Interest cost on projected benefit obligation	4		4		13		13
Expected return on plan assets	0		0		(1)		(1)
Amortization of net transition liability	1		1		2		3
Amortization of actuarial loss	3		2		9		6
Special termination costs	1		0		1		0
Net periodic cost	$ 11		$ 8		$ 29		$ 24

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