Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	$ 1,003,000,000	[1]	$ 783,000,000	[1]	$ 861,000,000	[1]
Capitalized interest	67,000,000		49,000,000		38,000,000
Credits to AFUDC debt and equity	25,000,000		25,000,000		16,000,000
Capitalized Software [Line Items]
Net unamortized software costs	499,000,000		280,000,000
Amortization of capitalized software costs	208,000,000		122,000,000		104,000,000
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Operating and maintenance	7,961,000,000		5,184,000,000		4,600,000,000
Interest Expense	903,000,000		701,000,000		792,000,000
Consolidation Percentages Detail Tagging [Abstract]
Percentage ownership of consolidated subsidiaries	100.00%
Exelon Percentage ownership of Exelon SHC, LLC	1.00%
Generation's percentage ownership in transmission company	12.50%
Percentage ownership of ComEd's common stock	99.00%
Percentage ownership of common stock	100.00%
Third-party monetary interest in subsidiaries	1,000,000
Third-party percentage interest in subsidiaries	12.50%
Minimum voting interest needed for a controlling financial interest	50.00%
New Site Development Costs [Abstract]
Capitalized development costs	1,300,000		376,000,000
Development costs expensed	4,200,000		2,000,000		6,000,000
Minimum [Member]
Consolidation Percentages Detail Tagging [Abstract]
Minimum voting interest needed for a controlling financial interest	20.00%
Maximum [Member]
Consolidation Percentages Detail Tagging [Abstract]
Minimum voting interest needed for a controlling financial interest	50.00%
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	368,000,000	[1]	219,000,000	[1]	191,000,000	[1]
Capitalized interest	67,000,000		49,000,000		38,000,000
Capitalized Software [Line Items]
Net unamortized software costs	143,000,000		82,000,000
Amortization of capitalized software costs	81,000,000		41,000,000		33,000,000
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Operating and maintenance	4,398,000,000		2,827,000,000		2,521,000,000
Interest Expense	301,000,000		170,000,000		153,000,000
Consolidation Percentages Detail Tagging [Abstract]
Percentage ownership of consolidated subsidiaries	100.00%
Generation's percentage ownership in transmission company	99.00%
Ownership Interest Upper Bound	99.00%
Ownership Interest Lower Bound	94.00%
Nuclear Fuel [Abstract]
Cost of spent nuclear fuel disposal per kWh of net nuclear generation	0.001
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	310,000,000	[1]	349,000,000	[1]	388,000,000	[1]
Credits to AFUDC debt and equity	9,000,000		12,000,000		5,000,000
Capitalized Software [Line Items]
Net unamortized software costs	105,000,000		120,000,000
Amortization of capitalized software costs	56,000,000		50,000,000		41,000,000
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Electrical transmission and distribution revenue	5,441,000,000		6,054,000,000		6,202,000,000
Operating and maintenance	1,182,000,000		1,031,000,000		917,000,000
Interest Expense	294,000,000		330,000,000		373,000,000
Consolidation Percentages Detail Tagging [Abstract]
Percentage ownership of consolidated subsidiaries	100.00%
Generation's percentage ownership in transmission company	75.00%
Third-party monetary interest in subsidiaries	1,000,000
Third-party percentage interest in subsidiaries	25.00%
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	125,000,000	[1]	138,000,000	[1]	197,000,000	[1]
Credits to AFUDC debt and equity	6,000,000		13,000,000		11,000,000
Capitalized Software [Line Items]
Net unamortized software costs	63,000,000		67,000,000
Amortization of capitalized software costs	30,000,000		25,000,000		19,000,000
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Operating and maintenance	698,000,000		698,000,000		644,000,000
Interest Expense	111,000,000		122,000,000		181,000,000
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	149,000,000	[1]	136,000,000	[1]	137,000,000	[1]
Credits to AFUDC debt and equity	15,000,000		22,000,000		16,000,000
Capitalized Software [Line Items]
Net unamortized software costs	157,000,000		62,000,000
Amortization of capitalized software costs	32,000,000		25,000,000		26,000,000
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Operating and maintenance	622,000,000		530,000,000		469,000,000
Interest Expense	144,000,000		129,000,000		131,000,000
Baltimore Gas and Electric Company [Member] | Restatement Adjustment [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Electrical transmission and distribution revenue	2,000,000
Operating and maintenance	3,000,000
Interest Expense	$ 5,000,000

[1] Exelon activity for the year ended December 31, 2012 includes the results of Constellation and BGE for March 12, 2012 – December 31, 2012. Generation activity for the year ended December 31, 2012 includes the results of Constellation for March 12, 2012 – December 31, 2012. BGE activity represents the activity for the years ended December 31, 2012, 2011 and 2010. (b)        Includes interest expense to affiliates.