Mergers, Acquisitions and Dispositions - Narrative (Details) - USD ($)				3 Months Ended												6 Months Ended	9 Months Ended		12 Months Ended
		Jun. 16, 2016	Dec. 31, 2014	Dec. 31, 2017	Dec. 31, 2016		Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Dec. 31, 2016		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014	Sep. 01, 2016	Mar. 24, 2016
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Asset																									$ 235,000,000
Payments to Acquire Businesses, Gross																				$ 6,934,000,000		$ 40,000,000	$ 386,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets											$ 1,441,000,000
Business Combination, Integration Related Costs	[1],[2]																			143,000,000		87,000,000
Share price											$ 27.25
Other Commitment					$ 513,000,000			$ 137,000,000								$ 137,000,000	$ 513,000,000			513,000,000
Revenues					7,875,000,000		$ 9,002,000,000	6,910,000,000	$ 7,573,000,000			$ 6,702,000,000	$ 7,401,000,000	$ 6,514,000,000	$ 8,830,000,000					31,360,000,000		29,447,000,000	27,429,000,000
Net income																				1,204,000,000		2,250,000,000	1,820,000,000
Merger and integration related costs																				558,000,000			44,000,000
Payments of Debt Restructuring Costs																						22,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent											$ 3,447,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets											248,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																									4,005,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities											1,515,000,000
Total net assets											7,142,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt											5,636,000,000
Other Intangible Assets [Member]
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired																				1,500,000,000
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Asset																									163,000,000
Payments to Acquire Businesses, Gross																				293,000,000		40,000,000	386,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets			$ 390,000,000																				390,000,000
Business Combination, Integration Related Costs	[2]																			37,000,000		24,000,000
Gain (Loss) on Disposition of Property Plant Equipment					69,000,000			10,000,000								32,000,000
Proceeds from Sale of Productive Assets		$ 37,000,000
Revenues					4,388,000,000		5,035,000,000	3,589,000,000	4,739,000,000			4,294,000,000	4,768,000,000	4,232,000,000	5,840,000,000					17,751,000,000		19,135,000,000	17,393,000,000
Net income																				558,000,000		1,340,000,000	1,019,000,000
Merger and integration related costs																				53,000,000			44,000,000
Payments of Debt Restructuring Costs																						0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent			(16,000,000)																				(16,000,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			50,000,000																				50,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities			(110,000,000)																				(110,000,000)
Asset Impairment Charges					23,000,000
Baltimore Gas and Electric Company [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2],[3]																			(1,000,000)		5,000,000
Revenues					812,000,000		812,000,000	680,000,000	929,000,000			746,000,000	725,000,000	628,000,000	1,036,000,000					3,233,000,000		3,135,000,000	3,165,000,000
Net income																				294,000,000		288,000,000	211,000,000
Merger and integration related costs																				0			0
Payments of Debt Restructuring Costs																						0
Baltimore Gas and Electric Company [Member] | Regulatory Assets [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs																				6,000,000
Commonwealth Edison Co [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2],[3]																			(6,000,000)		9,000,000
Other Additional Capital			5,000,000		158,000,000							7,000,000					158,000,000			158,000,000		7,000,000	5,000,000
Revenues					1,223,000,000		1,497,000,000	1,286,000,000	1,249,000,000			1,196,000,000	1,376,000,000	1,148,000,000	1,185,000,000					5,254,000,000		4,905,000,000	4,564,000,000
Net income					80,000,000		37,000,000	145,000,000	115,000,000			87,000,000	149,000,000	99,000,000	90,000,000					378,000,000		426,000,000	408,000,000
Merger and integration related costs																				0			0
Payments of Debt Restructuring Costs																						0
Commonwealth Edison Co [Member] | Regulatory Assets [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs																				8,000,000
PECO Energy Co [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2]																			5,000,000		4,000,000
Revenues					701,000,000		788,000,000	664,000,000	841,000,000			645,000,000	740,000,000	661,000,000	985,000,000					2,994,000,000		3,032,000,000	3,094,000,000
Net income																				438,000,000		378,000,000	352,000,000
Merger and integration related costs																				0			0
Payments of Debt Restructuring Costs																						0
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2],[3]																			28,000,000		3,000,000
Other Commitment									444,000,000
Pepco Holdings LLC [Member] | Regulatory Assets [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs																				16,000,000
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																				33,000,000
Gain (Loss) on Disposition of Property Plant Equipment												37,000,000				$ 8,000,000						9,000,000
Other Commitment					126,000,000												126,000,000			126,000,000
Revenues					491,000,000		635,000,000	509,000,000	551,000,000			488,000,000	592,000,000	504,000,000	545,000,000					2,186,000,000		2,129,000,000	2,055,000,000
Net income																				42,000,000		187,000,000	171,000,000
Merger and integration related costs																				125,000,000			0
Payments of Debt Restructuring Costs																						0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																									1,700,000,000
Potomac Electric Power Company [Member] | Regulatory Assets [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs																				11,000,000
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2]																			20,000,000		2,000,000
Gain (Loss) on Disposition of Property Plant Equipment					5,000,000		4,000,000
Other Commitment					86,000,000												86,000,000			86,000,000
Revenues					303,000,000		331,000,000	281,000,000	362,000,000			296,000,000	314,000,000	271,000,000	421,000,000					1,277,000,000		1,302,000,000	1,282,000,000
Net income																				(9,000,000)		76,000,000	104,000,000
Merger and integration related costs																				82,000,000			0
Payments of Debt Restructuring Costs																						0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																									1,100,000,000
Delmarva Power and Light Company [Member] | Regulatory Assets [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs																				4,000,000
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[2]																			19,000,000		1,000,000
Other Commitment					111,000,000												$ 111,000,000			111,000,000
Revenues					$ 275,000,000		421,000,000	270,000,000	291,000,000			291,000,000	386,000,000	285,000,000	334,000,000					1,257,000,000		1,295,000,000	1,210,000,000
Net income																				(42,000,000)		40,000,000	46,000,000
Merger and integration related costs																				110,000,000			0
Payments of Debt Restructuring Costs																						0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																									1,200,000,000
Preferred Stock [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																				180,000,000
Deferred Compensation, Share-based Payments [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	[4]																			$ 29,000,000
Minimum [Member]
Business Acquisition [Line Items]
Ownership interest					20.00%												20.00%			20.00%
Maximum [Member]
Business Acquisition [Line Items]
Ownership interest					50.00%												50.00%			50.00%
Predecessor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[3]										29,000,000									$ 19,000,000
Revenues											1,153,000,000	$ 1,126,000,000	$ 1,336,000,000	$ 1,119,000,000	$ 1,354,000,000							4,935,000,000	4,808,000,000
Net income											19,000,000											327,000,000	242,000,000
Merger and integration related costs											$ 0												0
Payments of Debt Restructuring Costs																						0
Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Asset					$ 400,000,000	[5]											$ 400,000,000	[5]		400,000,000	[5]				$ 235,000,000
Business Combination, Integration Related Costs	[3]																69,000,000
Other Commitment					323,000,000												323,000,000			323,000,000
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent					35,000,000												35,000,000			35,000,000
Revenues					1,078,000,000		1,394,000,000	$ 1,066,000,000	$ 105,000,000	[6]							3,643,000,000
Net income																	(61,000,000)
Merger and integration related costs																	317,000,000
Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment					24,000,000												24,000,000			24,000,000
Workforce Development [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Workforce Development [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Workforce Development [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Workforce Development [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment					50,000,000												50,000,000			50,000,000
Charitable Contributions [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Commitment					28,000,000												28,000,000			28,000,000
Charitable Contributions [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Commitment					12,000,000												12,000,000			12,000,000
Charitable Contributions [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Commitment					10,000,000												10,000,000			10,000,000
Charitable Contributions [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment					50,000,000												50,000,000			50,000,000
Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment					111,000,000												111,000,000			111,000,000
Energy Efficiency Program [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Energy Efficiency Program [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Energy Efficiency Program [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Energy Efficiency Program [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment					259,000,000												259,000,000			259,000,000
Rate Bill Credits [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Commitment					91,000,000												91,000,000			91,000,000
Rate Bill Credits [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Commitment					67,000,000												67,000,000			67,000,000
Rate Bill Credits [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Commitment					101,000,000												101,000,000			101,000,000
Rate Bill Credits [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment					259,000,000												259,000,000			259,000,000
Commitments [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Additional Capital					73,000,000												73,000,000			73,000,000
Commitments [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Additional Capital					46,000,000												46,000,000			46,000,000
Commitments [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Additional Capital					49,000,000												49,000,000			49,000,000
Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment					22,000,000												22,000,000			22,000,000
Delivery System Modernization [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Delivery System Modernization [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Delivery System Modernization [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Delivery System Modernization [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment					14,000,000												14,000,000			14,000,000
Green Sustainability Fund [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Green Sustainability Fund [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Green Sustainability Fund [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Green Sustainability Fund [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Other1 [Member]
Business Acquisition [Line Items]
Other Commitment					33,000,000												33,000,000			33,000,000
Other1 [Member] | Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Other Commitment					7,000,000												7,000,000			7,000,000
Other1 [Member] | Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Other Commitment					7,000,000												7,000,000			7,000,000
Other1 [Member] | Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Other Commitment					0												0			0
Other1 [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment					14,000,000												14,000,000			14,000,000
Delmarva Power and Light Company [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment					9,000,000												9,000,000			9,000,000
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Revenues																				3,785,000,000
Net income																				(66,000,000)
Pepco Holdings LLC [Member] | Preferred Stock [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																				180,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	[7]																62,000,000
Pepco Holdings LLC [Member] | Successor [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																	33,000,000
Pepco Holdings LLC [Member] | Successor [Member] | Deferred Compensation, Share-based Payments [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																	29,000,000
Pepco Holdings LLC [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Commitment					$ 513,000,000												$ 513,000,000			513,000,000
Pepco Holdings [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																				7,142,000,000
Intergrys Energy Group Inc [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			332,000,000
Business Combination, Bargain Purchase, Gain Recognized, Amount			28,000,000
Revenues			386,000,000
Net income			(42,000,000)
Merger and integration related costs																						$ 5,000,000	7,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities			$ 108,000,000																				$ 108,000,000
ConEdision [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																				235,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets																								$ 204,000,000
Payments to Acquire Businesses, Net of Cash Acquired																				22,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets																								1,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																								9,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities																								65,000,000
Total net assets																								$ 257,000,000
Fitzpatrick [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross							$ 110,000,000
Fitzpatrick [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Other Payments to Acquire Businesses																				$ 127,000,000
Fitzpatrick [Member] | Maximum [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs				$ 200,000,000															$ 250,000,000

[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] , includes the reversal of previously incurred acquisition, integration and financing costs of $8 million, $6 million, $11 million, $4 million, and $16 million incurred at ComEd, BGE, Pepco, DPL and PHI, respectively, that have been deferred and recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information.

[4] PHI’s unvested time-based restricted stock units and performance-based restricted stock units issued prior to April 29, 2014 were immediately vested and paid in cash upon the close of the merger. PHI’s remaining unvested time-based restricted stock units as of the close of the merger were cancelled. There were no remaining unvested performance-based restricted stock units as of the close of the merger.

[5] Distribution to member includes $235 million of net assets associated with PHI's unregulated business interests and $165 million of cash, each of which were distributed by PHI to Exelon.

[6] Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016.

[7] he liabilities assumed include $29 million for PHI stock-based compensation awards and $33 million for a merger related obligation, each assumed by PHI from Exelon. See Note 4 — Mergers, Acquisitions, and Dispositions.