Environmental Matters (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Disclosure Environmental Matters Details [Line Items]
Beginning Balance	$ 35	$ 42	$ 53
Amount accrued for environmental loss contingencies	10	21	16
Expenditures for environmental loss contingencies	(22)	(28)	(27)
Ending Balance	23	35	42
Period expected to be paid out over	one to 15 years	one to 15 years
PEF | Nitrogen Oxides
Emission Allowances Inventory [Line Items]
Emission allowances inventory	22	28
MGP And Other Sites
Disclosure Environmental Matters Details [Line Items]
Beginning Balance	20	22	31
Amount accrued for environmental loss contingencies	2	8	3
Expenditures for environmental loss contingencies	(5)	(10)	(12)
Ending Balance	17	20	22
MGP And Other Sites | PEC
Disclosure Environmental Matters Details [Line Items]
(Ward) site recorded liability	5	5
Site contingency, loss exposure not accrued	6
Site contingency, loss exposure not accrued, reimbursement	1
Remediation Of Distribution And Substation Transformers
Disclosure Environmental Matters Details [Line Items]
Beginning Balance	15	20	22
Amount accrued for environmental loss contingencies	8	13	13
Expenditures for environmental loss contingencies	(17)	(18)	(15)
Ending Balance	$ 6	$ 15	$ 20