Commitments and Contingencies - Commitments Narrative (Details) - Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] - Accrual For Environmental Loss Contingencies Material Components [Domain] - USD ($)	3 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Mar. 31, 2014	Jun. 30, 2012
Guarantor Obligations [Line Items]
Accrued environmental liabilities	$ 337,000,000	$ 347,000,000
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Accrued environmental liabilities	63,000,000	63,000,000
2016	583,000,000
2015	283,000,000
2018	185,000,000
Minimum future operating lease payments due in one year	0
Minimum future operating lease payments due in three years	12,000,000
Minimum future operating lease payments due in four years	13,000,000
Minimum future operating lease payments due in five years	13,000,000
Minimum future operating lease payments due beyond five years	285,000,000
Other Commitment	3,500,000
Loss Contingency, Loss in Period	44,000,000
Loss Contingency, Estimate of Possible Loss			$ 105,000,000
Operating Leases, Future Minimum Payments, Due in Two Years	5,000,000
Exelon Generation Co L L C [Member] | Combine-cycle Turbine Units [Member]
Guarantor Obligations [Line Items]
Other Commitment	736,000,000
Exelon Generation Co L L C [Member] | Fair Wind Project [Member]
Guarantor Obligations [Line Items]
Other Commitment	16,000,000
Exelon Generation Co L L C [Member] | Sendero Wind Project [Member]
Guarantor Obligations [Line Items]
Other Commitment	49,000,000
Exelon Generation Co L L C [Member] | AGE Biomass project [Member]
Guarantor Obligations [Line Items]
Other Commitment	170,000,000
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Accrued environmental liabilities	3,000,000	$ 1,000,000
Business Acquisition, Direct Investment With State And Local Governments Due To Settlement					$ 1,000,000,000
Loss Contingency, Estimate of Possible Loss	1,700,000
Minimum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Business Acquisition, Construction Cost				$ 95,000,000
Business Acquisition, Development Of New Generation Cost	575,000,000
Maximum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Business Acquisition, Construction Cost				$ 120,000,000
Business Acquisition, Development Of New Generation Cost	650,000,000
Equity Method Investments [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
2016	254,000,000
2015	77,000,000
2018	$ 7,000,000