Environmental Matters (Details) (USD $) In Millions	9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 MGP And Other Sites	Sep. 30, 2010 MGP And Other Sites	Sep. 30, 2011 MGP And Other Sites	Sep. 30, 2010 MGP And Other Sites	Sep. 30, 2011 Remediation Of Distribution And Substation Transformers	Sep. 30, 2010 Remediation Of Distribution And Substation Transformers	Sep. 30, 2011 Remediation Of Distribution And Substation Transformers	Sep. 30, 2010 Remediation Of Distribution And Substation Transformers	Sep. 30, 2011 PEC	Dec. 31, 2010 PEC	Sep. 30, 2011 PEF Nitrogen Oxides
Disclosure Environmental Matters Details [Line Items]
Beginning Balance	$ 35	$ 42			$ 20	$ 22			$ 15	$ 20
Amount accrued for environmental loss contingencies	7	18	0	0	1	7	0	0	6	11
Expenditures for environmental loss contingencies	(17)	(22)	0	0	(4)	(8)	0	(5)	(13)	(14)
Ending Balance	25	38	17	21	17	21	8	17	8	17
(Ward) site recorded liability											5	5
Site contingency, loss exposure not accrued											6
Site contingency, loss exposure not accrued, reimbursement											1
Emission Allowances Inventory [Line Items]
Reduction in value of emission allowances inventory													(23)
Regulatory asset recorded for reduction in value of emission allowances inventory													$ 22