Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions			3 Months Ended				6 Months Ended
		Mar. 31, 2016	Jun. 30, 2016	Jun. 30, 2016	Mar. 23, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 24, 2016
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						$ 1,432	$ 1,087
Regulatory assets	[1]						166	101
Amortization of intangible assets, net	[1]						28	24
Amortization of energy contract assets and liabilities	[2]						(7)	0
Nuclear fuel	[3]						557	552
Total depreciation, amortization and accretion							2,396	1,957
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			$ 160			$ 160	297	317
Gain (loss) on equity method investments							10	2
Provision for uncollectible accounts							51	80
Stock-based compensation costs							67	79
Other Decommissioning Related Activity	[4]						(123)	(50)
Energy-related options	[5]						(17)	27
Amortization of regulatory asset related to debt costs							4	0
Amortization of rate stabilization deferral							(34)	(40)
Amortization of debt fair value adjustment							(6)	(37)
Discrete impacts from EIMA	[6]						(21)	77
Amortization of debt costs							(14)	(35)
Merger related commitments	[7],[8]						503
Severance Obligation Severance Charges							122
Inventory Write-down							68
InventoryLCMReservePeriodCharge							36	13
Other							17	(4)
Total other noncash operating activities							1,056	579
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							(593)	(156)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG							0	95
Payments to Acquire Businesses, Gross							6,642	28
Capital Expenditures Incurred but Not yet Paid							(364)
Capitalized Costs, Asset Retirement Costs			471	$ 471			471
Asset Retirement Obligation, Accretion Expense	[9]						220	193
Capital Project [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							60
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						674	485
Amortization of intangible assets, net	[1]						23	24
Amortization of energy contract assets and liabilities	[2]						(7)	1
Nuclear fuel	[3]						557	552
Total depreciation, amortization and accretion							1,467	1,255
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			55			68	109	133
Gain (loss) on equity method investments							11	3
Provision for uncollectible accounts							13	11
Stock-based compensation costs							0	0
Other Decommissioning Related Activity	[4]						(123)	(50)
Energy-related options	[5]						(17)	27
Amortization of regulatory asset related to debt costs							0	0
Amortization of rate stabilization deferral							0	0
Amortization of debt fair value adjustment							(6)	(6)
Discrete impacts from EIMA							0	0
Amortization of debt costs							(10)	(8)
Merger related commitments	[8]						3
Severance Obligation Severance Charges							50
Inventory Write-down							66
InventoryLCMReservePeriodCharge							36	13
Other							17	(5)
Total other noncash operating activities							169	134
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							(217)	(155)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG	[8]						119
Payments to Acquire Businesses, Gross							1	28
Capital Expenditures Incurred but Not yet Paid							(317)
Capitalized Costs, Asset Retirement Costs			471	471			471
Asset Retirement Obligation, Accretion Expense	[9]						220	193
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							60
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						345	312
Regulatory assets	[1]						34	40
Total depreciation, amortization and accretion							379	352
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			42			51	83	103
Gain (loss) on equity method investments							0	0
Provision for uncollectible accounts							18	35
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	0
Amortization of rate stabilization deferral							0	0
Amortization of debt fair value adjustment							0	0
Discrete impacts from EIMA	[6]						(21)	77
Amortization of debt costs							(2)	(2)
Inventory Write-down							2
InventoryLCMReservePeriodCharge								0
Other							(3)	5
Total other noncash operating activities							83	222
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							38	26
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							(21)
Capitalized Costs, Asset Retirement Costs			0	0			0
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Contribution of Property	[10]						5	3
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						121	119
Regulatory assets	[1]						13	12
Total depreciation, amortization and accretion							134	131
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			8			10	17	19
Gain (loss) on equity method investments							0	0
Provision for uncollectible accounts							10	24
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							(1)	(1)
Inventory Write-down							0
InventoryLCMReservePeriodCharge								0
Other							(2)	1
Total other noncash operating activities							27	45
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							(96)	(60)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG							0
Capital Expenditures Incurred but Not yet Paid							(12)
Capitalized Costs, Asset Retirement Costs			0	0			0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						150	143
Regulatory assets	[1]						56	49
Total depreciation, amortization and accretion							206	192
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			18			17	33	33
Gain (loss) on equity method investments							0	0
Provision for uncollectible accounts							3	11
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							(34)	(40)
Amortization of debt fair value adjustment							0	0
Discrete impacts from EIMA							0	0
Amortization of debt costs							(2)	(1)
Inventory Write-down							0
InventoryLCMReservePeriodCharge								0
Other							(12)	(9)
Total other noncash operating activities							60	76
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							(3)	61
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG							0
Capital Expenditures Incurred but Not yet Paid							2
Capitalized Costs, Asset Retirement Costs			0	0			0
Asset Retirement Obligation, Accretion Expense							0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						85	81
Regulatory assets	[1]						59	44
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							144	125
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	[11]		7			7	16	15
Gain (loss) on equity method investments							0	0
Provision for uncollectible accounts							8	9
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	1
Amortization of rate stabilization deferral							2	(8)
Amortization of debt fair value adjustment							0	0
Discrete impacts from EIMA							0	0
Amortization of debt costs							0	0
Merger related commitments	[8]						138
Inventory Write-down							1
Other							(4)	0
Total other noncash operating activities							158	33
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							(47)	(36)
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
Asset Retirement Obligation, Accretion Expense	[9]						0	0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						55	50
Regulatory assets	[1]						21	24
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							4
Total depreciation, amortization and accretion							76	74
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	[11]		4			4	9	8
Gain (loss) on equity method investments							0	0
Provision for uncollectible accounts							8	12
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							(2)	(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]						100
Inventory Write-down							1
Other							(3)	1
Total other noncash operating activities							121	22
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							(51)	(4)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG							0
Capital Expenditures Incurred but Not yet Paid							(9)
Asset Retirement Obligation, Accretion Expense	[9]						0	0
Asset Retirement Obligation, Revision of Estimate							(4)
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]						40	38
Regulatory assets	[1]						41	48
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							81	86
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	[11]		4			4	8	8
Gain (loss) on equity method investments							0	0
Provision for uncollectible accounts							10	9
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							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]						120
Inventory Write-down							1
Other							(3)	0
Total other noncash operating activities							138	17
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities							(110)	(24)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG							0
Capital Expenditures Incurred but Not yet Paid							6
Asset Retirement Obligation, Accretion Expense	[9]						0	0
Asset Retirement Obligation, Revision of Estimate							$ (2)
Pepco Holdings LLC [Member]
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			$ 27	31
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			193
Regulatory assets	[1]				58			114
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			307
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense					23	$ 24		48
Gain (loss) on equity method investments					0
Provision for uncollectible accounts					16			30
Stock-based compensation costs					3			6
Other Decommissioning Related Activity					0			0
Energy-related options					0			0
Amortization of regulatory asset related to debt costs					1			2
Amortization of rate stabilization deferral					(5)			(9)
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)			4
Total other noncash operating activities					46			101
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities					(9)			(63)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Asset Retirement Obligation, Accretion Expense	[9]				$ 0			$ 0
Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	$ 111
Regulatory assets	[1]	63
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		174		174
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				31
Gain (loss) on equity method investments				0
Provision for uncollectible accounts				7
Stock-based compensation costs				0
Other Decommissioning Related Activity				0
Energy-related options				0
Amortization of regulatory asset related to debt costs				1
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]			358
Severance Obligation Severance Charges				54
Inventory Write-down				0
Other				(7)
Total other noncash operating activities				444
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(237)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG				127
Business Combination, Contingent Consideration, Liability, Noncurrent									$ 53
Capital Expenditures Incurred but Not yet Paid				(4)
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				62
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		$ 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

[11] Pepco's, DPL's, ACE's and PHISCO's pension and postretirement benefit costs for the six months ended June 30, 2016 include $7 million, $4 million, $3 million and $9 million, respectively, of costs incurred prior to the closing of Exelon’s merger with PHI on March 23, 2016.