Commitments and Contingencies - Commitments Narrative (Details) (USD $)	9 Months Ended													9 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013		Sep. 30, 2014 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member]		Jun. 30, 2012 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Beebe Construction [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Perryman Construction [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Fourmile Construction [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Combine-cycle Turbine Units [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Minimum [Member] Exelon Generation Co L L C [Member] MW	Sep. 30, 2013 Minimum [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Maximum [Member] Exelon Generation Co L L C [Member] MW	Sep. 30, 2013 Maximum [Member] Exelon Generation Co L L C [Member]	Sep. 30, 2014 Equity Method Investments [Member] Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Accrued environmental liabilities										$ 6,000,000
2015				578,000,000							75,000,000							86,000,000
2014				104,000,000								7,000,000						27,000,000
2017				303,000,000									334,000,000					20,000,000
Business Acquisition, Direct Investment With State And Local Governments Due To Settlement									1,000,000,000
Business Acquisition, Construction Cost															95,000,000		120,000,000
Minimum future operating lease payments due in one year				0
Minimum future operating lease payments due in three years				10,000,000
Minimum future operating lease payments due in four years				12,000,000
Minimum future operating lease payments due in five years				13,000,000
Minimum future operating lease payments due beyond five years				290,000,000
Business Acquisition, Development Of New Generation Cost														600,000,000		650,000,000
Business Acquisition, Expected New Generation Mwh														285		300
Noncash Merger Related Costs	$ 44,000,000	$ (6,000,000)	[1]	$ 44,000,000	$ 0	[1]	$ (6,000,000)	[1]								$ 105,000,000

[1] Relates to integration costs to achieve distribution synergies related to the Constellation merger transaction that were reclassified to a regulatory asset. See Note 5 — Regulatory Matters for more information.