Commitments and Contingencies - Commitments Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Mar. 31, 2014	Jun. 30, 2012
Guarantor Obligations [Line Items]
Accrued environmental liabilities	$ 376,000,000	$ 376,000,000		$ 347,000,000
Noncash Merger Related Costs			$ 44,000,000
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Accrued environmental liabilities	63,000,000	63,000,000		63,000,000
Minimum future operating lease payments due in one year	0	0
Minimum future operating lease payments due in three years	12,000,000	12,000,000
Minimum future operating lease payments due in four years	13,000,000	13,000,000
Minimum future operating lease payments due in five years	13,000,000	13,000,000
Minimum future operating lease payments due beyond five years	285,000,000	285,000,000
Noncash Merger Related Costs			44,000,000
Other Commitment	3,500,000	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	5,000,000
Costs Incurred, Development Costs		353,000,000
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Accrued environmental liabilities	3,000,000	3,000,000		$ 1,000,000
Business Acquisition, Direct Investment With State And Local Governments Due To Settlement						$ 1,000,000,000
Noncash Merger Related Costs			$ 0
Loss Contingency, Estimate of Possible Loss	1,700,000	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	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	650,000,000
Equity Method Investments [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
2016	276,000,000	276,000,000
2015	38,000,000	38,000,000
2018	$ 7,000,000	$ 7,000,000