Derivative Financial Instruments (Collateral and Contingent-Related Features) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Collateral And Contingent Related Features [Abstract]
Line Of Credit Facility Amount Outstanding	$ 1,821.00
Swap Contract Collateral Posting Limit [Abstract]
Fair value of interest-rate swap in asset position	30.00
Exelon Generation Co L L C [Member]
Collateral And Contingent Related Features [Abstract]
Aggregate fair value of derivatives with credit-risk-related contingent features	(1,849.00)	(1,014.00)
Contractual right of offset related to derivative assets	1,426.00	928.00
Net liability position after contractual right of offset	(423.00)	(86.00)
Incremental collateral for credit rating downgrade to BBB- and Baa3	1,920.00	1,612.00
Cash collateral held	499.00	542.00
Cash collateral posted	527.00
Letters of credit held	45.00	89.00
Letters of credit posted	563.00
Line Of Credit Facility Amount Outstanding	1,818.00
Swap Contract Collateral Posting Limit [Abstract]
Swap contract collateral posting limit	200.00
Fair value of interest-rate swap in asset position	17.00
Commonwealth Edison Co [Member]
Collateral And Contingent Related Features [Abstract]
Cash collateral held	19.00
Swap Contract Collateral Posting Limit [Abstract]
Swap contract collateral posting limit	200.00
PECO Energy Co [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	35.00
Line Of Credit Facility Amount Outstanding	1.00
Baltimore Gas and Electric Company [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for loss of investment grade credit rating	124.00
Other Segment [Member]
Collateral And Contingent Related Features [Abstract]
Incremental collateral for credit rating downgrade to BBB- and Baa3	$ 1,920.00