Commitments and Contingencies - Commitments Narrative (Details) $ in Millions		3 Months Ended
		Mar. 31, 2016 USD ($) MW	Mar. 31, 2015 USD ($)	Jun. 30, 2013 USD ($)
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 53
Noncash Merger Related Costs	[1],[2]	503
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Noncash Merger Related Costs	[2]	3
Costs Incurred, Development Costs		398
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Business Acquisition, Direct Investment With State And Local Governments Due To Settlement				$ 1,000
Minimum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Business Acquisition, Construction Cost			$ 95
Business Acquisition, Development Of New Generation Cost		$ 500
Business Acquisition, Expected New Generation Mwh | MW		275
Maximum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Business Acquisition, Construction Cost			$ 120
Business Acquisition, Development Of New Generation Cost		$ 600
Business Acquisition, Expected New Generation Mwh | MW		300
Noncash Merger Related Costs		$ 105

[1] (e)Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.

[2] See Note 4 — Mergers, Acquisitions and Dispositions for additional information related to the merger with PHI.