Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Related Party Transactions [Line Items]
Guarantees of future financial or performance assurance on behalf of its subsidiaries	$ 453
Guarantee obligations related party	300
Money pool, weighted average interest rate	0.32%	0.30%	0.74%
PESC to PEC
Related Party Transactions [Line Items]
Affiliated services	203	176	170
Combustion turbine transfer		24
PESC to PEF
Related Party Transactions [Line Items]
Affiliated services	160	156	147
PEC to PEF
Related Party Transactions [Line Items]
Affiliated services	57	43	36
PEF to PEC
Related Party Transactions [Line Items]
Affiliated services	$ 12	18	12