Debt and Credit Facilities - Debt and Credit Facilities (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended		3 Months Ended			9 Months Ended			3 Months Ended	9 Months Ended	3 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Parent	Dec. 31, 2010 Parent	Mar. 31, 2011 Senior Notes Parent	Sep. 30, 2011 PEC	Dec. 31, 2010 PEC	Sep. 30, 2011 PEC First Mortgage Bonds Due September 15, 2021	Sep. 30, 2011 PEF	Dec. 31, 2010 PEF	Jun. 30, 2011 PEF First Mortgage Bonds Due July 15, 2011	Sep. 30, 2011 PEF First Mortgage Bonds Due August 15, 2021	Mar. 31, 2011 Senior Notes Due March 1, 2011	Jun. 30, 2011 Original Expiration
Long-term debt [Line Items]
Debt instrument, face amount					$ 500			$ 500				$ 300
Maturity date					Jan. 15, 2021			Sep. 15, 2021			Jul. 15, 2011	Aug. 15, 2021	Mar. 01, 2011
Current portion of long-term debt	(950)	(505)				(500)	0		0	(300)
Long-term debt, net	11,717	11,864				3,693	3,693		4,482	4,182
Long-term debt, affiliate	273	273
Maturities of debt											300		700
Debt instrument issuance date					January 21, 2011			September 15, 2011				August 18, 2011
Debt instrument, interest rate stated percentage					4.40%			3.00%			6.65%	3.10%	7.10%
RCAs and available capacity [Line Items]
RCA expiration date			May 3, 2011
RCA total			478	500										22
RCA available	1,978
Short Term Debt [Line Items]
Short-term debt	$ 45	$ 0