Commitments and Contingencies - Commitments Narrative (Details) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($) MW	Jun. 30, 2013 USD ($)
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 50	$ 50
Noncash Merger Related Costs	[1],[2]		$ 508
Power Volume | MW			220
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Noncash Merger Related Costs	[2]		$ 3
Costs Incurred, Development Costs		404
Minimum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Business Acquisition, Development Of New Generation Cost		450	$ 450
Business Acquisition, Expected New Generation Mwh | MW			275
Maximum [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Business Acquisition, Development Of New Generation Cost		550	$ 550
Business Acquisition, Expected New Generation Mwh | MW			300
Noncash Merger Related Costs			$ 105
Equity Unit Purchase Agreements [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
2015		$ 25	$ 25
Merger Commitment [Member]
Guarantor Obligations [Line Items]
Investments				$ 1,000
Merger Commitment [Member] | Minimum [Member]
Guarantor Obligations [Line Items]
Investments				0
Merger Commitment [Member] | Maximum [Member]
Guarantor Obligations [Line Items]
Investments				$ 0

[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.