Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended	9 Months Ended
		Jun. 30, 2016	Mar. 23, 2016	Mar. 22, 2016	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Mar. 24, 2016	Dec. 31, 2015
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					$ 2,490	$ 1,648
Regulatory assets	[1]					293	131
Amortization of intangible assets, net	[1]					38	39
Amortization of energy contract assets and liabilities	[2]					(7)	(20)
Nuclear fuel	[3]					862	841
Total depreciation, amortization and accretion						4,009	2,930
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense						458	476
Gain (loss) on equity method investments						15	3
Provision for uncollectible accounts						107	114
Stock-based compensation costs						88	102
Other Decommissioning Related Activity	[4]					(237)	(31)
Energy-related options	[5]					(20)	18
Amortization of regulatory asset related to debt costs						7	0
Amortization of rate stabilization deferral						62	60
Amortization of debt fair value adjustment						(9)	(34)
Discrete impacts from EIMA	[6]					(36)	101
Amortization of debt costs						26	43
Merger related commitments	[7],[8]					508
Inventory Write-down						74	7
InventoryLCMReservePeriodCharge						36	15
Restructuring Costs						130
Other						15	(18)
Total other noncash operating activities						1,224	856
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						(537)	(322)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0	95
Payments to Acquire Businesses, Gross						6,896	28
Capital Expenditures Incurred but Not yet Paid						(338)	(59)
Capitalized Costs, Asset Retirement Costs					$ 476	476			$ 811
Asset Retirement Obligation, Accretion Expense	[9]					333	291
Capital Project [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						84
Nuclear Fuel Project [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					1,297	739
Amortization of intangible assets, net	[1]					32	35
Amortization of energy contract assets and liabilities	[2]					(7)	(19)
Nuclear fuel	[3]					862	841
Total depreciation, amortization and accretion						2,516	1,887
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense						163	200
Gain (loss) on equity method investments						16	4
Provision for uncollectible accounts						14	15
Stock-based compensation costs						0	0
Other Decommissioning Related Activity	[4]					(237)	(31)
Energy-related options	[5]					(20)	18
Amortization of regulatory asset related to debt costs						0	0
Amortization of rate stabilization deferral						0	0
Amortization of debt fair value adjustment						(9)	(9)
Discrete impacts from EIMA						0	0
Amortization of debt costs						12	12
Merger related commitments	[8]					3
Inventory Write-down						70	8
InventoryLCMReservePeriodCharge						36	15
Restructuring Costs						57
Other						24	(5)
Total other noncash operating activities						129	227
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						(204)	(245)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG	[8]					119
Payments to Acquire Businesses, Gross						255	28
Capital Expenditures Incurred but Not yet Paid						(289)	(48)
Capitalized Costs, Asset Retirement Costs					476	476			811
Asset Retirement Obligation, Accretion Expense	[9]					332	291
Exelon Generation Co L L C [Member] | Capital Project [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						84
Exelon Generation Co L L C [Member] | Nuclear Fuel Project [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					524	471
Regulatory assets	[1]					49	57
Total depreciation, amortization and accretion						574	528
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense						124	155
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						31	46
Stock-based compensation costs						0	0
Other Decommissioning Related Activity						0	0
Energy-related options						0	0
Amortization of regulatory asset related to debt costs						3	0
Amortization of rate stabilization deferral						0	0
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA	[6]					(36)	101
Amortization of debt costs						(3)	3
Inventory Write-down						4	0
InventoryLCMReservePeriodCharge							0
Other						(1)	7
Total other noncash operating activities						122	312
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						104	34
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0	0
Capital Expenditures Incurred but Not yet Paid						(42)	(62)
Capitalized Costs, Asset Retirement Costs					0	0			0
Asset Retirement Obligation, Accretion Expense	[9]					1
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Contribution of Property	[10]					157	5
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					181	179
Regulatory assets	[1]					20	19
Total depreciation, amortization and accretion						201	198
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense						25	29
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						24	37
Stock-based compensation costs						0	0
Other Decommissioning Related Activity						0	0
Energy-related options						0	0
Amortization of regulatory asset related to debt costs						1	0
Amortization of rate stabilization deferral						0	0
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA						0	0
Amortization of debt costs						2	2
Inventory Write-down						0	0
InventoryLCMReservePeriodCharge							0
Other						(3)	1
Total other noncash operating activities						49	69
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						(49)	(16)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0	0
Capital Expenditures Incurred but Not yet Paid						(4)	23
Capitalized Costs, Asset Retirement Costs					0	0			0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					223	216
Regulatory assets	[1]					84	55
Total depreciation, amortization and accretion						307	271
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense						50	49
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						12	15
Stock-based compensation costs						0	0
Other Decommissioning Related Activity						0	0
Energy-related options						0	0
Amortization of regulatory asset related to debt costs						0	0
Amortization of rate stabilization deferral						62	60
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA						0	0
Amortization of debt costs						3	2
Inventory Write-down						0	0
InventoryLCMReservePeriodCharge							0
Other						18	15
Total other noncash operating activities						109	111
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						(2)	(28)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0	0
Capital Expenditures Incurred but Not yet Paid						17	(14)
Capitalized Costs, Asset Retirement Costs					0	0			0
Asset Retirement Obligation, Accretion Expense						0
PEPCO Holdings Inc [Member] | Predecessor [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capitalized Costs, Asset Retirement Costs									0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					128	122
Regulatory assets	[1]					93	69
Amortization of intangible assets, net	[1]					0	0
Amortization of energy contract assets and liabilities	[2]					0	0
Nuclear fuel	[3]					0	0
Total depreciation, amortization and accretion						221	191
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				$ 7		24	22
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						15	15
Stock-based compensation costs						0	0
Other Decommissioning Related Activity						0	0
Energy-related options						0	0
Amortization of regulatory asset related to debt costs						2	2
Amortization of rate stabilization deferral						3	3
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA						0	0
Amortization of debt costs						0	0
Merger related commitments	[8]					125
Inventory Write-down						1	0
Other						(2)	0
Total other noncash operating activities						168	42
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						(83)	(94)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0	0
Capital Expenditures Incurred but Not yet Paid						15	1
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense	[9]					0	0
Potomac Electric Power Company [Member] | Successor [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Payments to Acquire Businesses, Gross						33
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					82	76
Regulatory assets	[1]					38	37
Amortization of intangible assets, net	[1]					0	0
Amortization of energy contract assets and liabilities	[2]					0	0
Nuclear fuel	[3]					0	0
Asset retirement obligation accretion						5
Total depreciation, amortization and accretion						120	113
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				4		13	11
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						12	18
Stock-based compensation costs						0	0
Other Decommissioning Related Activity						0	0
Energy-related options						0	0
Amortization of regulatory asset related to debt costs						0	0
Amortization of rate stabilization deferral						3	1
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA						0	0
Amortization of debt costs						0	0
Merger related commitments	[8]					73
Inventory Write-down						1	0
Other						(8)	1
Total other noncash operating activities						99	31
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						(70)	(22)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0	0
Capital Expenditures Incurred but Not yet Paid						(10)	(2)
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense	[9]					0	0
Asset Retirement Obligation, Revision of Estimate						(5)
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					61	57
Regulatory assets	[1]					69	78
Amortization of intangible assets, net	[1]					0	0
Amortization of energy contract assets and liabilities	[2]					0	0
Nuclear fuel	[3]					0	0
Asset retirement obligation accretion						2
Total depreciation, amortization and accretion						130	135
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				$ 3		11	11
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						18	15
Stock-based compensation costs						0	0
Other Decommissioning Related Activity						0	0
Energy-related options						0	0
Amortization of regulatory asset related to debt costs						1	0
Amortization of rate stabilization deferral						0	0
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA						0	0
Amortization of debt costs						0	0
Merger related commitments	[8]					110
Inventory Write-down						1	0
Other						(5)	1
Total other noncash operating activities						138	27
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities						(87)	8
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0	0
Capital Expenditures Incurred but Not yet Paid						2	0
Capitalized Costs, Asset Retirement Costs									$ 0
Asset Retirement Obligation, Accretion Expense	[9]					0	0
Asset Retirement Obligation, Revision of Estimate						(2)
Pepco Holdings LLC [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			$ 0
Capital Expenditures Incurred but Not yet Paid			11
Pepco Holdings LLC [Member] | Predecessor [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		94				292
Regulatory assets	[1]		58				182
Amortization of intangible assets, net	[1]		0				0
Amortization of energy contract assets and liabilities	[2]		0				0
Nuclear fuel	[3]		0				0
Total depreciation, amortization and accretion			152				474
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			23				73
Gain (loss) on equity method investments			0
Provision for uncollectible accounts			16				49
Stock-based compensation costs			3				9
Other Decommissioning Related Activity			0				0
Energy-related options			0				0
Amortization of regulatory asset related to debt costs			1				4
Amortization of rate stabilization deferral			5				3
Amortization of debt fair value adjustment			0				0
Discrete impacts from EIMA			0				0
Amortization of debt costs			0				1
Inventory Write-down			1				1
Other			(3)				3
Total other noncash operating activities			46				143
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(9)				(112)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG							0
Capital Expenditures Incurred but Not yet Paid							3
Asset Retirement Obligation, Accretion Expense	[9]		$ 0				$ 0
Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]				215
Regulatory assets	[1]				140
Amortization of intangible assets, net	[1]				0
Amortization of energy contract assets and liabilities	[2]				0
Nuclear fuel	[3]				0
Total depreciation, amortization and accretion					355
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense					58
Gain (loss) on equity method investments					0
Provision for uncollectible accounts					27
Stock-based compensation costs					0
Other Decommissioning Related Activity					0
Energy-related options					0
Amortization of regulatory asset related to debt costs					2
Amortization of rate stabilization deferral					0
Amortization of debt fair value adjustment					0
Discrete impacts from EIMA					0
Amortization of debt costs					0
Merger related commitments	[8]				308
Inventory Write-down					0
Restructuring Costs					(53)
Other					(7)
Total other noncash operating activities					441
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities					(248)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG					129
Business Combination, Contingent Consideration, Liability, Noncurrent								$ 53
Capital Expenditures Incurred but Not yet Paid					(5)
Asset Retirement Obligation, Accretion Expense	[9]				0
Pepco Holdings LLC [Member] | Successor [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Payments to Acquire Businesses, Gross		$ 33			62
Deferred Compensation, Share-based Payments [Member] | Pepco Holdings LLC [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Payments to Acquire Businesses, Gross						$ 29
Deferred Compensation, Share-based Payments [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Payments to Acquire Businesses, Gross					$ 29

[1] (a)Included in Depreciation and amortization on the Registrants' Consolidated Statements of Operations and Comprehensive Income.

[2] (b)Included in Operating revenues or Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

[3] Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

[4] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 16 - Asset Retirement Obligations of the Exelon 2015 Form 10-K for additional information regarding the accounting for nuclear decommissioning

[5] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded

[6] Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 5 — Regulatory Matters for more information

[7] (e)Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.

[8] See Note 4 — Mergers, Acquisitions and Dispositions for additional information related to the merger with PHI.

[9] Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

[10] See Note 11— Income Taxes for discussion of the like-kind exchange tax position