Mergers, Acquisitions, and Dispositions - Narrative (Details) $ / shares in Units, MW in Millions, $ in Millions					3 Months Ended			6 Months Ended
		May 02, 2016 USD ($)	Apr. 21, 2016 USD ($)	Mar. 23, 2016 USD ($)	Jun. 30, 2017 USD ($) MW	Jun. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) MW	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Mar. 24, 2016 USD ($) $ / shares
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross								$ 212	$ 6,642
Business Combination, Bargain Purchase, Gain Recognized, Amount					$ 0	$ 0		226	0
Business Combination, Integration Related Costs	[1],[2]				8	1		17	103
Other Commitment					3,086			3,086
Impairment of Long-Lived Assets to be Disposed of								418
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
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
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred								293
Business Combination, Bargain Purchase, Gain Recognized, Amount								226
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred								110
Business Combination, Consideration Transferred, Other								129
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								212	1
Business Combination, Bargain Purchase, Gain Recognized, Amount					0	0		226	0
Business Combination, Integration Related Costs	[2]				4	4		13	20
Other Commitment					2,257			2,257
Members' Capital					9,308			9,308		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								293
Business Combination, Consideration Transferred, Other								183
Payments to Acquire Businesses, Gross								293
Business Combination, Integration Related Costs					16			47
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								239
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]
Payments to Acquire Businesses, Gross							$ 33
Business Combination, Integration Related Costs	[2],[3]				2	(1)	55
Members' Capital					8,828			8,828		$ 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]
Payments to Acquire Businesses, Gross									33
Business Combination, Integration Related Costs	[2],[4]				1	(4)		2	23
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],[5]				0	0		(7)	16
Other Commitment					11			11
Goodwill					1,100			1,100
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]				1	2		2	15
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] 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] (g)For the six months ended June 30, 2017, includes the reversal of previously incurred acquisition, integration and financing costs of $8 million incurred at PHI that have been deferred and recorded as a regulatory asset for anticipated recovery. For the three months ended June 30, 2016 and the Successor period March 24, 2016 to June 30, 2016, includes the reversal of previously incurred acquisition, integration and financing costs of $12 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.

[4] (e)For the three and six months ended June 30, 2016, includes the reversal of previously incurred acquisition, integration and financing costs of $9 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.

[5] (f)For the six months ended June 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 three and six months ended June 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.