Environmental Matters (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	$ 23		$ 35
Amount accrued for environmental loss contingencies	16		7
Expenditures for environmental loss contingencies	(7)		(17)
Ending Balance	32	[1]	25	[1]
Maximum [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Cost of new control equipment estimate	320
Minimum [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Cost of new control equipment estimate	150
PEC [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	11		12
Amount accrued for environmental loss contingencies	4		0
Expenditures for environmental loss contingencies	(2)		(1)
Ending Balance	13	[2]	11	[2]
PEC [Member] | MGP Site [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Amount accrued for environmental loss contingencies	7
PEC [Member] | MGP Site [Member] | Maximum [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Site contingency, loss exposure in excess of accrual, high estimate	25
PEF [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	12		23
Amount accrued for environmental loss contingencies	12		7
Expenditures for environmental loss contingencies	(5)		(16)
Ending Balance	19	[1]	14	[1]
Cost of new control equipment estimate	1,000
PEF [Member] | Orlando MGP OU1 [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Amount accrued for environmental loss contingencies	9
Site contingency, loss exposure in excess of accrual, high estimate	$ 8

[1] Expected to be paid out over one to 12 years.

[2] Expected to be paid out over one to ten years.