Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions			3 Months Ended
		Mar. 31, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2015		Mar. 31, 2015
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			$ 606					$ 540
Regulatory assets			65					58
Amortization of intangible assets, net			14					12
Amortization of energy contract assets and liabilities	[1]		(14)					(31)
Nuclear fuel	[2]		283					272
Asset retirement obligation accretion	[3]		109					97
Total depreciation, amortization and accretion			1,063					948
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			136					159
Gain (loss) on equity method investments			(3)
Provision for uncollectible accounts			41					84
Stock-based compensation costs			44					39
Other Decommissioning Related Activity	[4]		(55)					(44)
Energy-related options	[5]		(9)					9
Amortization of regulatory asset related to debt costs			1					3
Amortization of rate stabilization deferral			20					25
Amortization of debt fair value adjustment			(3)					(9)
Discrete impacts from EIMA	[6]		14					(46)
Amortization of debt costs			8					18
Merger related commitments	[7],[8]		503
Severance Obligation Severance Charges			69
Inventory Write-down			1					10
Other			23					4
Inventory Adjustments		$ 36	36
Total other noncash operating activities			804					344
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(311)					(250)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			0
Capital Expenditures Incurred but Not yet Paid			(290)
Capitalized Costs, Asset Retirement Costs		62	62			$ 56
Gains (Losses) on Extinguishment of Debt			(2)
Capital Project [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired			31
Successor [Member]
Other Non-Cash Operating Activities [Abstract]
Merger related commitments	[8]	358
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			278					242
Amortization of intangible assets, net			11					12
Amortization of energy contract assets and liabilities	[1]		(14)					(32)
Nuclear fuel	[2]		283					272
Asset retirement obligation accretion	[3]		109					97
Total depreciation, amortization and accretion			667					591
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			54	[9]		67	[9]	67
Gain (loss) on equity method investments			(3)
Provision for uncollectible accounts			6					4
Stock-based compensation costs			0					0
Other Decommissioning Related Activity	[4]		(55)					(44)
Energy-related options	[5]		(9)					9
Amortization of regulatory asset related to debt costs			0					0
Amortization of rate stabilization deferral			0					0
Amortization of debt fair value adjustment			(3)					(4)
Discrete impacts from EIMA			0					0
Amortization of debt costs			4					4
Merger related commitments	[8]		3
Severance Obligation Severance Charges			4
Inventory Write-down			1					10
Other			7					(1)
Inventory Adjustments		36	36
Total other noncash operating activities			51					45
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(148)					(232)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG	[8]		119
Capital Expenditures Incurred but Not yet Paid			(234)
Capitalized Costs, Asset Retirement Costs		62	62			56
Gains (Losses) on Extinguishment of Debt			(2)
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			31
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			170					154
Regulatory assets			19					21
Total depreciation, amortization and accretion			189					175
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			41			52		52
Gain (loss) on equity method investments			0
Provision for uncollectible accounts			9					22
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					2
Amortization of rate stabilization deferral			0					0
Amortization of debt fair value adjustment			0					0
Discrete impacts from EIMA	[6]		14					(46)
Amortization of debt costs			1					1
Inventory Write-down			0					0
Other			(6)					3
Total other noncash operating activities			32					126
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			14					9
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			0
Capital Expenditures Incurred but Not yet Paid			25
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]		1					2
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			60					58
Regulatory assets			7					4
Total depreciation, amortization and accretion			67					62
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			8			10		10
Gain (loss) on equity method investments			0
Provision for uncollectible accounts			16					33
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					1
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					0
Other			(1)					(1)
Total other noncash operating activities			24					44
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(95)					(70)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			0
Capital Expenditures Incurred but Not yet Paid			(65)
Capitalized Costs, Asset Retirement Costs		0	0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			75					71
Regulatory assets			34					35
Asset retirement obligation accretion			0
Total depreciation, amortization and accretion			109					106
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			16			17		16
Gain (loss) on equity method investments			0
Provision for uncollectible accounts			12					25
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			20					25
Amortization of debt fair value adjustment			0					0
Discrete impacts from EIMA			0					0
Amortization of debt costs			1					1
Inventory Write-down			0					0
Other			(5)					(3)
Total other noncash operating activities			44					64
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(30)					99
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			0
Capital Expenditures Incurred but Not yet Paid			(4)
Capitalized Costs, Asset Retirement Costs		0	0			0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			42					40
Regulatory assets			33					22
Amortization of intangible assets, net			0					0
Amortization of energy contract assets and liabilities	[1]		0					0
Nuclear fuel	[2]		0					0
Asset retirement obligation accretion	[3]		0					0
Total depreciation, amortization and accretion			75					62
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			8					8
Gain (loss) on equity method investments			0
Provision for uncollectible accounts			5					4
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			1					10
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					0
Other			(1)					0
Total other noncash operating activities			153					23
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(9)					(18)
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
Capitalized Costs, Asset Retirement Costs						0
PEPCO Holdings Inc [Member]
Other Non-Cash Operating Activities [Abstract]
Severance Obligation Severance Charges		52
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG		127			$ 0
Capital Expenditures Incurred but Not yet Paid		(7)			11
PEPCO Holdings Inc [Member] | Predecessor [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment					94			96
Regulatory assets					58			59
Amortization of intangible assets, net					0			0
Amortization of energy contract assets and liabilities	[1]				0			0
Nuclear fuel	[2]				0			0
Asset retirement obligation accretion	[3]				0			0
Total depreciation, amortization and accretion					152			155
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense					23			24
Gain (loss) on equity method investments					0
Provision for uncollectible accounts					16			16
Stock-based compensation costs					3			3
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					5			11
Amortization of debt fair value adjustment					0			0
Discrete impacts from EIMA					0			0
Amortization of debt costs					0			0
Inventory Write-down					1			0
Other					(3)			2
Total other noncash operating activities					$ 46			57
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capitalized Costs, Asset Retirement Costs						0
PEPCO Holdings Inc [Member] | Successor [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment		9
Regulatory assets		5
Amortization of intangible assets, net		0
Amortization of energy contract assets and liabilities	[1]	0
Nuclear fuel	[2]	0
Asset retirement obligation accretion	[3]	0
Total depreciation, amortization and accretion		14
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense		3
Gain (loss) on equity method investments		0
Provision for uncollectible accounts		(2)
Stock-based compensation costs		0
Other Decommissioning Related Activity		0
Energy-related options		0
Amortization of regulatory asset related to debt costs		0
Amortization of rate stabilization deferral		0
Amortization of debt fair value adjustment		0
Discrete impacts from EIMA		0
Amortization of debt costs		0
Inventory Write-down		0
Other		(1)
Total other noncash operating activities		410
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			27					25
Regulatory assets			12					14
Amortization of intangible assets, net			0					0
Amortization of energy contract assets and liabilities	[1]		0					0
Nuclear fuel	[2]		0					0
Asset retirement obligation accretion	[3]		0					0
Total depreciation, amortization and accretion			39					39
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			5					4
Gain (loss) on equity method investments			0
Provision for uncollectible accounts			5					7
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			4					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					0
Other			(1)					0
Total other noncash operating activities			118					12
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(9)					14
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			0
Capital Expenditures Incurred but Not yet Paid			8
Capitalized Costs, Asset Retirement Costs		4	4			0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			20					19
Regulatory assets			20					24
Amortization of intangible assets, net			0					0
Amortization of energy contract assets and liabilities	[1]		0					0
Nuclear fuel	[2]		0					0
Asset retirement obligation accretion	[3]		0					0
Total depreciation, amortization and accretion			40					43
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense			4					4
Gain (loss) on equity method investments			0
Provision for uncollectible accounts			7					5
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					0
Other			(2)					(1)
Total other noncash operating activities			132					8
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities			(3)					$ 20
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)
Capitalized Costs, Asset Retirement Costs		$ 2	$ 2			$ 0

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

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

[3] Included in Operating and maintenance 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 to results of operations

[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] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmI4M2MxNDE3MDYxODRkNzQ5ZTcwNzJlZThlYmU3MWU2fFRleHRTZWxlY3Rpb246N0QzMjIzMURGRDVBNjNBQTgzRjZGQkE2NTU2RDY2MjkM}

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