Mergers, Acquisitions, and Dispositions - Narrative (Details) $ / shares in Units, MW in Millions, $ in Millions			3 Months Ended				12 Months Ended
		Mar. 31, 2016 USD ($) MW	Mar. 31, 2017 USD ($) MW		Mar. 31, 2016 USD ($)		Dec. 31, 2016 USD ($)		Mar. 24, 2016 USD ($) $ / shares
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue					$ 8,556	[1]	$ 32,342	[2]
Revenues			$ 8,757		7,573
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross			(212)		(6,645)
Business Combination, Integration Related Costs	[3],[4]		9		102
Other Commitment			3,212
Net income			981		123
Business Combination, Bargain Purchase, Gain Recognized, Amount			226		0
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Revenues			1,200		107
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Cash offered in exchange for each share of PHI stock | $ / shares									$ 27.25
Other Commitment			513
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	[5]		4,005
Business Combination, Contingent Consideration, Asset									$ 235
Net income			140		(315)
Pepco Holdings LLC [Member] | Other Intangible Assets [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Finite-lived Intangible Assets Acquired			$ 1,500
Pepco Holdings LLC [Member] | Common Stock [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross		$ (6,933)
Pepco Holdings LLC [Member] | Common Stock [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross		$ (180)
Pepco Holdings LLC [Member] | Other Solar Projects [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
OtherNonFinancialCommitment1 | MW		37	27
Pepco Holdings LLC [Member] | Wind Assets [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
OtherNonFinancialCommitment1 | MW		100
Pepco Holdings LLC [Member] | Other Investments [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment									137
PEPCO Holdings Inc [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross		$ (7,142)
Other Commitment			$ 513
PEPCO Holdings Inc [Member] | Other Investments [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment			444
Fitzpatrick [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Bargain Purchase, Gain Recognized, Amount			226
Business Combination, Consideration Transferred			293
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Consideration Transferred			110
Business Combination, Consideration Transferred, Other			129
Fitzpatrick [Member] | Nuclear Fuel [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Consideration Transferred, Other			54
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Revenues			4,888		4,739
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross			(212)		(1)
Business Combination, Integration Related Costs	[4]		9		16
Other Commitment			2,404
Net income			409		257
Members' Capital			9,310				9,261
Business Combination, Bargain Purchase, Gain Recognized, Amount			226		0
Exelon Generation Co L L C [Member] | Pepco Holdings LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Contingent Consideration, Asset									163
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross			(302)
Business Combination, Integration Related Costs			32
Business Combination, Consideration Transferred			293
Business Combination, Consideration Transferred, Other			183
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross			(248)
Business Combination, Consideration Transferred			110
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Nuclear Fuel [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross			(54)
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Accounts Receivable [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross			(9)
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Revenues			275		291
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	[4]		1		13
Other Commitment			8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			1,200
Net income			28		(100)
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment			111
Equity Contribution		49
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Revenues			530		551
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment			15
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			1,700
Net income			58		(108)
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment			126
Equity Contribution		73
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Revenues			362		362
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	[4]		(7)	[6]	16
Other Commitment			11
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			1,100
Net income			57		(72)
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment			85
Equity Contribution		46
Pepco Holdings LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	[4]		1		$ 27
Pepco Holdings LLC [Member] | Scenario, Adjustment [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent									59
Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Revenues		105	1,175
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs		56	(5)
Net income		$ (309)	140
Members' Capital			8,577				$ 8,077		$ 7,200
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment			$ 322

[1] The amounts above include adjustments for non-recurring costs directly related to the merger of $639 million and intercompany revenue of $170 million for the three months ended March 31, 2016.

[2] The amounts above include adjustments for non-recurring costs directly related to the merger of $680 million and intercompany revenue of $171 million for the year ended December 31, 2016.

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

[4] 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.

[5] 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.

[6] 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.