Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
		Mar. 23, 2016	Mar. 31, 2015	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 24, 2016
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						$ 1,340,000,000	$ 930,000,000	$ 940,000,000
Income taxes (net of refunds)						(441,000,000)	342,000,000	314,000,000
Pension and non-pension postretirement benefit costs						619,000,000	637,000,000	560,000,000
Income (Loss) from Equity Method Investments						24,000,000	7,000,000	0
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions						0	0	20,000,000
IncomeLossFromEquityMethodInvestmentsNonCash								22,000,000
Provision for uncollectible accounts						155,000,000	120,000,000	156,000,000
Provision for excess and obsolete inventory						12,000,000	10,000,000	5,000,000
Stock-based compensation costs						111,000,000	97,000,000	91,000,000
Other decommissioning related-activity						(384,000,000)	(82,000,000)	(132,000,000)
Energy-related options						(11,000,000)	21,000,000	122,000,000
Amortization of regulatory asset related to debt costs						9,000,000	7,000,000	11,000,000
Amortization of rate stabilization deferral						76,000,000	73,000,000	65,000,000
Amortization of debt fair value adjustment						(11,000,000)	(17,000,000)	(23,000,000)
Merger-related commitments (c)(d)						558,000,000		44,000,000
Restructuring Costs						99,000,000
Asset Retirement Obligation, Revision of Estimate						2,000,000
Amortization of Debt Issuance Costs						35,000,000	144,000,000	53,000,000
Discrete impacts from EIMA						8,000,000	58,000,000	53,000,000
Lower of cost or market inventory adjustment						37,000,000	23,000,000	29,000,000
Litigation Settlement, Amount						(28,000,000)
Proceeds from Collection of Other Receivables						(13,000,000)
Other						35,000,000	11,000,000	(2,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						1,333,000,000	1,109,000,000	1,054,000,000
Other Noncash Expense							77,000,000
Change in PPE related to ARO update				$ 191,000,000		191,000,000	885,000,000	72,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(128,000,000)	(96,000,000)	(220,000,000)
Payments to Acquire Businesses, Gross						6,934,000,000	40,000,000	386,000,000
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						(54,000,000)
Consolidated VIE dividend to noncontrolling								4,000,000
Fair value of net assets recorded upon CENG consolidation								3,400,000,000
Issuance of equity units								(131,000,000)
Contribution of Property								0
Non Cash Licensing Agreement							95,000,000
Antelope Valle [Member]
Supplemental Cash Flow Information [Line Items]
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							(170,000,000)
Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						(95,000,000)
Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								70,000,000
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							(57,000,000)
Contribution of Property						0	0
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						339,000,000	348,000,000	322,000,000
Income taxes (net of refunds)						435,000,000	476,000,000	227,000,000
Pension and non-pension postretirement benefit costs						218,000,000	269,000,000	249,000,000
Income (Loss) from Equity Method Investments			$ (19,000,000)			0	0	20,000,000
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions						25,000,000	8,000,000	0
IncomeLossFromEquityMethodInvestmentsNonCash								(20,000,000)
Provision for uncollectible accounts						19,000,000	22,000,000	14,000,000
Provision for excess and obsolete inventory						6,000,000	9,000,000	5,000,000
Stock-based compensation costs						0	0	0
Other decommissioning related-activity						(384,000,000)	(82,000,000)	(132,000,000)
Energy-related options						(11,000,000)	21,000,000	122,000,000
Amortization of regulatory asset related to debt costs						0	0	0
Amortization of rate stabilization deferral						0	0	0
Amortization of debt fair value adjustment						(11,000,000)	(17,000,000)	(23,000,000)
Merger-related commitments (c)(d)						53,000,000		44,000,000
Restructuring Costs						22,000,000
Asset Retirement Obligation, Revision of Estimate					$ 285,000,000		1,300,000,000
Amortization of Debt Issuance Costs						17,000,000	15,000,000	12,000,000
Discrete impacts from EIMA						0	0	0
Lower of cost or market inventory adjustment						36,000,000	23,000,000	29,000,000
Other						25,000,000	0	6,000,000
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						15,000,000	268,000,000	346,000,000
Other Noncash Expense							77,000,000
Change in PPE related to ARO update				191,000,000		191,000,000	885,000,000	72,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(50,000,000)	(82,000,000)	(61,000,000)
Payments to Acquire Businesses, Gross						293,000,000	40,000,000	386,000,000
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						(54,000,000)
Consolidated VIE dividend to noncontrolling								645,000,000
Fair value of net assets recorded upon CENG consolidation								3,400,000,000
Issuance of equity units								0
Contribution of Property								0
Exelon Generation Co L L C [Member] | Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						(95,000,000)
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								70,000,000
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							(57,000,000)
Contribution of Property						0	0
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						298,000,000	308,000,000	292,000,000
Income taxes (net of refunds)						(444,000,000)	(265,000,000)	(6,000,000)
Pension and non-pension postretirement benefit costs						166,000,000	206,000,000	162,000,000
Income (Loss) from Equity Method Investments						0	0
IncomeLossFromEquityMethodInvestmentsNonCash								0
Provision for uncollectible accounts						41,000,000	53,000,000	26,000,000
Provision for excess and obsolete inventory						4,000,000	1,000,000	0
Stock-based compensation costs						0	0	0
Other decommissioning related-activity						0	0	0
Energy-related options						0	0	0
Amortization of regulatory asset related to debt costs						4,000,000	5,000,000	8,000,000
Amortization of rate stabilization deferral						0	0	0
Amortization of debt fair value adjustment						0	0	0
Merger-related commitments (c)(d)						0		0
Restructuring Costs						0
Amortization of Debt Issuance Costs						4,000,000	4,000,000	4,000,000
Discrete impacts from EIMA						8,000,000	144,000,000	53,000,000
Lower of cost or market inventory adjustment						0	0
Other						(12,000,000)	3,000,000	2,000,000
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						215,000,000	416,000,000	255,000,000
Change in PPE related to ARO update				0		0	0	0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(91,000,000)	(34,000,000)	(78,000,000)
Fair value of net assets recorded upon CENG consolidation								0
Issuance of equity units								0
Contribution of Property								5,000,000
Commonwealth Edison Co [Member] | Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						0
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Contribution of Property						158,000,000	7,000,000
PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						104,000,000	94,000,000	94,000,000
Income taxes (net of refunds)						64,000,000	64,000,000	85,000,000
Pension and non-pension postretirement benefit costs						33,000,000	39,000,000	36,000,000
Income (Loss) from Equity Method Investments						0	0
IncomeLossFromEquityMethodInvestmentsNonCash								0
Provision for uncollectible accounts						30,000,000	30,000,000	52,000,000
Provision for excess and obsolete inventory						0	0	0
Stock-based compensation costs						0	0	0
Other decommissioning related-activity						0	0	0
Energy-related options						0	0	0
Amortization of regulatory asset related to debt costs						1,000,000	2,000,000	3,000,000
Amortization of rate stabilization deferral						0	0	0
Amortization of debt fair value adjustment						0	0	0
Merger-related commitments (c)(d)						0		0
Amortization of Debt Issuance Costs						3,000,000	2,000,000	2,000,000
Discrete impacts from EIMA						0	0	0
Lower of cost or market inventory adjustment						1,000,000	0
Other						(3,000,000)	(3,000,000)	(1,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						65,000,000	70,000,000	92,000,000
Change in PPE related to ARO update				0		0	0	0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(11,000,000)	(13,000,000)	0
Fair value of net assets recorded upon CENG consolidation								0
Issuance of equity units								0
Contribution of Property								0
PECO Energy Co [Member] | Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						0
PECO Energy Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Contribution of Property						0	0
Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						92,000,000	120,000,000	111,000,000
Income taxes (net of refunds)						31,000,000	73,000,000	(21,000,000)
Pension and non-pension postretirement benefit costs						67,000,000	65,000,000	64,000,000
Income (Loss) from Equity Method Investments						0	0
IncomeLossFromEquityMethodInvestmentsNonCash								0
Provision for uncollectible accounts						1,000,000	15,000,000	64,000,000
Provision for excess and obsolete inventory						0	0	0
Stock-based compensation costs						0	0	0
Other decommissioning related-activity						0	0	0
Energy-related options						0	0	0
Amortization of regulatory asset related to debt costs						0	0	0
Amortization of rate stabilization deferral						81,000,000	73,000,000	65,000,000
Amortization of debt fair value adjustment						0	0	0
Merger-related commitments (c)(d)						0		0
Amortization of Debt Issuance Costs						1,000,000	2,000,000	2,000,000
Discrete impacts from EIMA						0	0	0
Lower of cost or market inventory adjustment						0	0
Litigation Settlement, Amount						(28,000,000)
Proceeds from Collection of Other Receivables						(13,000,000)
Other						(21,000,000)	(18,000,000)	(15,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						88,000,000	137,000,000	180,000,000
Change in PPE related to ARO update				0		0	0	0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(86,000,000)	(9,000,000)	(25,000,000)
Fair value of net assets recorded upon CENG consolidation								0
Issuance of equity units								0
Contribution of Property								0
Baltimore Gas and Electric Company [Member] | Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						0
Baltimore Gas and Electric Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Contribution of Property						0	0
Pepco Holdings LLC [Member]
Supplemental Cash Flow Information [Line Items]
Litigation Settlement, Amount						1,600,000
Pepco Holdings LLC [Member] | Deferred Compensation, Share-based Payments [Member]
Supplemental Cash Flow Information [Line Items]
Payments to Acquire Businesses, Gross	[1]					29,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)				209,000,000
Income taxes (net of refunds)				258,000,000
Pension and non-pension postretirement benefit costs				86,000,000
Income (Loss) from Equity Method Investments				0
Provision for uncollectible accounts				65,000,000
Provision for excess and obsolete inventory				1,000,000
Stock-based compensation costs				0
Other decommissioning related-activity				0
Energy-related options				0
Amortization of regulatory asset related to debt costs				3,000,000
Amortization of rate stabilization deferral				(5,000,000)
Amortization of debt fair value adjustment				0
Merger-related commitments (c)(d)				317,000,000
Restructuring Costs				56,000,000
Asset Retirement Obligation, Revision of Estimate				2,000,000
Amortization of Debt Issuance Costs				1,000,000
Discrete impacts from EIMA				0
Lower of cost or market inventory adjustment				0
Other				(12,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities				514,000,000
Change in PPE related to ARO update									$ 0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash				(21,000,000)
NonCashFairValueAdjustment				127,000,000
Business Combination, Contingent Consideration, Liability, Noncurrent									$ 53,000,000
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		$ 43,000,000					268,000,000	257,000,000
Income taxes (net of refunds)		11,000,000					(13,000,000)	(2,000,000)
Pension and non-pension postretirement benefit costs		23,000,000					97,000,000	58,000,000
Income (Loss) from Equity Method Investments		0					0
IncomeLossFromEquityMethodInvestmentsNonCash								0
Provision for uncollectible accounts		16,000,000					61,000,000	49,000,000
Provision for excess and obsolete inventory		1,000,000					1,000,000	0
Stock-based compensation costs		3,000,000					13,000,000	18,000,000
Other decommissioning related-activity		0					0	0
Energy-related options		0					0	0
Amortization of regulatory asset related to debt costs		1,000,000					5,000,000	5,000,000
Amortization of rate stabilization deferral		5,000,000					(2,000,000)	2,000,000
Amortization of debt fair value adjustment		0					0	0
Merger-related commitments (c)(d)		0						0
Restructuring Costs		0
Amortization of Debt Issuance Costs		0					2,000,000	1,000,000
Discrete impacts from EIMA		0						0
Lower of cost or market inventory adjustment		0					0
Other		(3,000,000)					(10,000,000)	(6,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities		46,000,000					167,000,000	127,000,000
Change in PPE related to ARO update		0					0	0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash		(11,000,000)					(6,000,000)	(28,000,000)
Fair value of net assets recorded upon CENG consolidation								0
Issuance of equity units								0
Contribution of Property								0
Pepco Holdings LLC [Member] | Indemnification Agreement [Member] | Successor [Member]
Supplemental Cash Flow Information [Line Items]
Contribution of Property				0
Pepco Holdings LLC [Member] | Indemnification Agreement [Member] | Predecessor [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Contribution of Property		$ 0
Potomac Electric Power Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						118,000,000	116,000,000	111,000,000
Income taxes (net of refunds)						216,000,000	(6,000,000)	(58,000,000)
Pension and non-pension postretirement benefit costs						31,000,000	30,000,000	22,000,000
Income (Loss) from Equity Method Investments						0	0
IncomeLossFromEquityMethodInvestmentsNonCash								0
Provision for uncollectible accounts						29,000,000	21,000,000	17,000,000
Provision for excess and obsolete inventory						3,000,000	0	0
Stock-based compensation costs						0	0	0
Other decommissioning related-activity						0	0	0
Energy-related options						0	0	0
Amortization of regulatory asset related to debt costs						2,000,000	2,000,000	3,000,000
Amortization of rate stabilization deferral						(12,000,000)	1,000,000	3,000,000
Amortization of debt fair value adjustment						0	0	0
Merger-related commitments (c)(d)						125,000,000		0
Amortization of Debt Issuance Costs							0	0
Discrete impacts from EIMA							0	0
Lower of cost or market inventory adjustment							0
Other						5,000,000	0	(8,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						183,000,000	54,000,000	37,000,000
Change in PPE related to ARO update				0		0	0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(27,000,000)	(1,000,000)	(10,000,000)
Payments to Acquire Businesses, Gross						33,000,000
Fair value of net assets recorded upon CENG consolidation								0
Issuance of equity units								0
Potomac Electric Power Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Contribution of Property							0
Delmarva Power and Light Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						47,000,000	47,000,000	45,000,000
Income taxes (net of refunds)						115,000,000	(5,000,000)	(43,000,000)
Pension and non-pension postretirement benefit costs						18,000,000	15,000,000	7,000,000
Income (Loss) from Equity Method Investments						0	0
IncomeLossFromEquityMethodInvestmentsNonCash								0
Provision for uncollectible accounts						23,000,000	20,000,000	14,000,000
Provision for excess and obsolete inventory						1,000,000	0	0
Stock-based compensation costs						0	0	0
Other decommissioning related-activity						0	0	0
Energy-related options						0	0	0
Amortization of regulatory asset related to debt costs						1,000,000	1,000,000	2,000,000
Amortization of rate stabilization deferral						2,000,000	(3,000,000)	(1,000,000)
Amortization of debt fair value adjustment						0	0	0
Merger-related commitments (c)(d)						82,000,000		0
Asset Retirement Obligation, Revision of Estimate						1,000,000
Amortization of Debt Issuance Costs							0	0
Discrete impacts from EIMA							0	0
Lower of cost or market inventory adjustment							0
Other						(14,000,000)	0	0
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						114,000,000	33,000,000	22,000,000
Change in PPE related to ARO update				0		0	0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(12,000,000)	(3,000,000)	(8,000,000)
Fair value of net assets recorded upon CENG consolidation								0
Issuance of equity units								0
Delmarva Power and Light Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Contribution of Property							0
Atlantic City Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)						62,000,000	63,000,000	61,000,000
Income taxes (net of refunds)						200,000,000	0	(3,000,000)
Pension and non-pension postretirement benefit costs						15,000,000	15,000,000	13,000,000
Income (Loss) from Equity Method Investments						0	0
IncomeLossFromEquityMethodInvestmentsNonCash								0
Provision for uncollectible accounts						32,000,000	20,000,000	13,000,000
Provision for excess and obsolete inventory						1,000,000	0	0
Stock-based compensation costs						0	0	0
Other decommissioning related-activity						0	0	0
Energy-related options						0	0	0
Amortization of regulatory asset related to debt costs						1,000,000	1,000,000	0
Amortization of rate stabilization deferral						0	0	0
Amortization of debt fair value adjustment						0	0	0
Merger-related commitments (c)(d)						110,000,000		0
Asset Retirement Obligation, Revision of Estimate						2,000,000
Amortization of Debt Issuance Costs							0	0
Discrete impacts from EIMA							0	0
Lower of cost or market inventory adjustment							0
Other						(6,000,000)	1,000,000	0
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities						155,000,000	37,000,000	26,000,000
Change in PPE related to ARO update				0		0	0
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash						(11,000,000)	(3,000,000)	(9,000,000)
Fair value of net assets recorded upon CENG consolidation								0
Issuance of equity units								0
Atlantic City Electric Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options								$ 0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Contribution of Property						$ 0	0
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Cash Flow Information [Line Items]
Payments to Acquire Businesses, Gross	[2]			62,000,000
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Cash Flow Information [Line Items]
Payments to Acquire Businesses, Gross				33,000,000
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Successor [Member] | Deferred Compensation, Share-based Payments [Member]
Supplemental Cash Flow Information [Line Items]
Payments to Acquire Businesses, Gross				$ 29,000,000
Severance [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Cash Flow Information [Line Items]
Discrete impacts from EIMA							$ 0

[1] 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.

[2] 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.