Basis of Presentation (Details) (USD $)																							3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Letters of credit	Mar. 31, 2012 Carrying amounts of investments	Mar. 31, 2012 Debt and payment guarantees	Mar. 31, 2012 Power contract monetization entities	Mar. 31, 2012 Power contract monetization entities Letters of credit	Mar. 31, 2012 All Other VIEs	Mar. 31, 2012 All Other VIEs Carrying amounts of investments	Mar. 31, 2012 All Other VIEs Debt and payment guarantees	Mar. 31, 2012 Exelon Generation Co L L C [Member] VIE	Dec. 31, 2011 Exelon Generation Co L L C [Member] VIE	Mar. 31, 2012 Exelon Generation Co L L C [Member] Letters of credit	Mar. 31, 2012 Exelon Generation Co L L C [Member] Carrying amounts of investments	Mar. 31, 2012 Exelon Generation Co L L C [Member] Debt and payment guarantees	Mar. 31, 2012 Exelon Generation Co L L C [Member] Power contract monetization entities	Mar. 31, 2012 Exelon Generation Co L L C [Member] Power contract monetization entities Letters of credit	Mar. 31, 2012 Exelon Generation Co L L C [Member] All Other VIEs	Mar. 31, 2012 Exelon Generation Co L L C [Member] All Other VIEs Carrying amounts of investments	Mar. 31, 2012 Exelon Generation Co L L C [Member] All Other VIEs Debt and payment guarantees	Mar. 31, 2012 Baltimore Gas and Electric Company [Member]	Dec. 31, 2011 Baltimore Gas and Electric Company [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] RSB BondCo. LLC	Mar. 31, 2011 Baltimore Gas and Electric Company [Member] RSB BondCo. LLC
Consolidated Variable Interest Entity [Abstract]
Remittance of payments received from customers for rate stabilization to BondCo.																							$ 20,000,000	$ 23,000,000
Parental guarantee provided																					75,000,000
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets	525,000,000	0									474,000,000	0									50,000,000	30,000,000
Noncurrent assets	410,000,000	0									364,000,000	0									0	0
Total Assets	935,000,000	0									838,000,000	0									50,000,000	30,000,000
Current liabilities	415,000,000	0									340,000,000	0									74,000,000	69,000,000
Noncurrent liabilities	606,000,000	0									228,000,000	0									332,000,000	331,000,000
Total Liabilities	1,021,000,000	0									568,000,000	0									406,000,000	400,000,000
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of Variable Interest Entities not consolidated by equity holders											6	6
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	636,000,000					286,000,000		350,000,000			636,000,000					286,000,000		350,000,000
Total liabilities	336,000,000					223,000,000		113,000,000			336,000,000					223,000,000		113,000,000
Our ownership interest	94,000,000							94,000,000			94,000,000							94,000,000
Other ownership interests	206,000,000					63,000,000		143,000,000			206,000,000					63,000,000		143,000,000
Our maximum exposure to loss			$ 14,000,000	$ 76,000,000	$ 5,000,000		$ 14,000,000		$ 76,000,000	$ 5,000,000			$ 14,000,000	$ 76,000,000	$ 5,000,000		$ 14,000,000		$ 76,000,000	$ 5,000,000