Mergers, Acquisitions, and Dispositions - Narrative (Details) $ / shares in Units, MW in Millions, $ in Millions							1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended
		Mar. 31, 2017 USD ($)	Sep. 01, 2016 USD ($)	May 02, 2016 USD ($)	Apr. 21, 2016 USD ($)	Mar. 23, 2016 USD ($)	Jul. 31, 2016 USD ($)	Sep. 30, 2017 USD ($) MW	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) MW	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Mar. 24, 2016 USD ($) $ / shares
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross											$ 208	$ 6,896
Business Combination, Bargain Purchase, Gain Recognized, Amount								$ 7	$ 0		233	0
Business Combination, Integration Related Costs	[1],[2]							(8)	20		10	123
Other Commitment								2,879			2,879
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						$ 7,142
Other Commitment								$ 513			513		$ 513
Cash offered in exchange for each share of PHI stock | $ / shares														$ 27.25
Goodwill						4,005
Business Combination, Contingent Consideration, Asset														$ 235
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	[3]					7,142
Pepco Holdings LLC [Member] | Other Intangible Assets [Member]
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired											$ 1,500
Pepco Holdings LLC [Member] | Other Solar Projects [Member]
Business Acquisition [Line Items]
OtherNonFinancialCommitment1 | MW								27			37
Pepco Holdings LLC [Member] | Wind Assets [Member]
Business Acquisition [Line Items]
OtherNonFinancialCommitment1 | MW											100
Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment								$ 8			$ 8
Pepco Holdings LLC [Member] | Net present value [Member]
Business Acquisition [Line Items]
Other Commitment													444
Pepco Holdings LLC [Member] | Other commitments [Member]
Business Acquisition [Line Items]
Other Investments								137			137
ConEdison Solutions [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 257
Net Working Capital			204
Goodwill			100
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			$ 257
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 289
Business Combination, Bargain Purchase, Gain Recognized, Amount								7			233
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		522
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		110
Business Combination, Consideration Transferred, Other		125
Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other		54
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross											208	255
Business Combination, Bargain Purchase, Gain Recognized, Amount								7	0		233	0
Business Combination, Integration Related Costs	[2]							5	9		18	29
Other Commitment								2,272			2,272
Members' Capital								9,357			9,357		9,261
Gain (Loss) on Disposition of Property Plant Equipment					$ 32
Exelon Generation Co L L C [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Asset														163
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		289
Business Combination, Consideration Transferred, Other		179
Payments to Acquire Businesses, Gross											289
Business Combination, Integration Related Costs								6			53
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net								3			3
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 110
Payments to Acquire Businesses, Gross								4			235
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross											54
Pepco Holdings LLC [Member] | Scenario, Adjustment [Member]
Business Acquisition [Line Items]
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent														59
Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2],[4]							(15)	7	$ 63
Members' Capital								8,835			8,835		$ 8,077	$ 7,200
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								315			315
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2],[5]							(8)	3		(6)	26
Other Commitment								20			20
Goodwill								1,700			1,700
Gain (Loss) on Disposition of Property Plant Equipment				$ 8
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								120			120
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment								6			6
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Other commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital									73	73		73
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2],[6]							1	2		(6)	18
Other Commitment								11			11
Goodwill								1,100			1,100
Gain (Loss) on Disposition of Property Plant Equipment							$ 4
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								84			84
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment								2			2
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member] | Other commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital									46	46		46
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2]							(8)	2		(6)	17
Other Commitment								9			9
Goodwill								1,200			1,200
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								$ 111			$ 111
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Other commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital									$ 49	$ 49		$ 49
Preferred Stock [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						$ 180

[1] .

[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] Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.

[4] For the three and nine months ended September 30, 2017, includes the reversal of previously incurred acquisition, integration and financing costs of $16 million and $24 million, respectively, incurred at PHI that have been deferred and recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to September 30, 2016, includes the reversal of previously incurred acquisition, integration and financing costs of $13 million incurred at PHI that have been deferred and recorded as a regulatory asset for anticipated recovery. See Note 5—Regulatory Matters for more information.

[5] For the three and nine months ended September 30, 2017, includes the reversal of previously incurred acquisition, integration and financing costs of $8 million incurred at Pepco that have been deferred and recorded as a regulatory asset for anticipated recovery. For the nine months ended September 30, 2016, includes the reversal of previously incurred acquisition, integration and financing costs of $10 million incurred at Pepco that have been deferred and recorded as a regulatory asset for anticipated recovery. See Note 5—Regulatory Matters for more information.

[6] For the nine months ended September 30, 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. For the nine months ended September 30, 2016, includes the reversal of previously incurred acquisition, integration and financing costs of $3 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.