Purchase Obligations (Details) (Fuel for production, USD $) In Millions	12 Months Ended
	Dec. 31, 2010
PEC | Pipeline transportation capacity costs
Purchase Obligations [Line Items]
Unrecorded unconditional purchase obligation, date range	May 2011 through April 2031
Contractual obligations less than one year	$ 16
Contractual obligations one to three years	49
Contractual obligations three to five years	49
Contractual obligations more than five years	373
Long term contract amount, total	487
PEC | Conditional agreement
Purchase Obligations [Line Items]
Unrecorded unconditional purchase obligation, date range	May 2011 through May 2033
Long term contract amount, total	2,042
PEF | Pipeline transportation capacity costs
Purchase Obligations [Line Items]
Unrecorded unconditional purchase obligation, date range	April 2011 through April 2036
Contractual obligations less than one year	36
Contractual obligations one to three years	95
Contractual obligations three to five years	95
Contractual obligations more than five years	945
Long term contract amount, total	$ 1,171