Mergers, Acquisitions, and Dispositions Merger Integration Related Costs Table (Details) - USD ($) $ in Millions			3 Months Ended
		Mar. 31, 2016	Mar. 31, 2017		Mar. 31, 2016		Mar. 23, 2016
Business Combination, Integration Related Costs	[1],[2]		$ 9		$ 102
Exelon Generation Co L L C [Member]
Business Combination, Integration Related Costs	[2]		9		16
Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs	[2]		0		(8)	[3]
PECO Energy Co [Member]
Business Combination, Integration Related Costs	[2]		1		2
Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs	[2]		2		2
Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	[2]		1		27
Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs	[2]		(7)	[4]	16
Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs	[2]		1		13
Successor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs		$ 56	(5)
Predecessor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs							$ 29
Regulatory Assets [Member] | Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs					$ 9
Regulatory Assets [Member] | Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs			$ 8

[1] Reflects costs (benefits) recorded at Exelon related to financing, including mark-to-market activity on forward-starting interest rate swaps.

[2] The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above.

[3] For the three months ended March 31, 2016, includes the reversal of previously incurred acquisition, integration and financing costs of $9 million, incurred at ComEd that have been deferred and recorded as a regulatory asset for anticipated recovery. See Note 5—Regulatory Matters for more information.

[4] For the three months ended March 31, 2017, includes the reversal of previously incurred acquisition, integration and financing costs of $8 million, incurred at DPL that have been deferred and recorded as a regulatory asset for anticipated recovery. See Note 5—Regulatory Matters for more information.