Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions				3 Months Ended
		Mar. 31, 2016		Mar. 31, 2017		Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2016
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			$ 754		$ 606
Regulatory assets	[1]			128		65
Amortization of intangible assets, net	[1]			14		14
Amortization of Power Contracts Emission Credits	[2]			2		(14)
Asset retirement obligation accretion						0
Total depreciation, amortization and accretion				1,274		1,063
Amortization of Nuclear Fuel Lease	[3]			264		283
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				157		136
Gain (loss) on equity method investments				10		3
Provision for uncollectible accounts				34		41
Stock-based compensation costs				31		44
Other Decommissioning Related Activity	[4]			(84)		(55)
Energy-related options	[5]			(4)		(9)
Amortization of regulatory asset related to debt costs				2		1
Amortization of rate stabilization deferral				(14)		20
Amortization of debt fair value adjustment				(5)		(3)
Discrete impacts from EIMA	[6]			(24)		(14)
Amortization of debt costs				9		8
Merger related commitments						503
Inventory Write-down				2		1
InventoryLCMReservePeriodCharge						36
Restructuring Costs						69
Other				4		23
Total other noncash operating activities				118		804
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(439)		(311)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0
Payments to Acquire Businesses, Gross				212		6,645
Capital Expenditures Incurred but Not yet Paid				(298)		(290)
Capitalized Costs, Asset Retirement Costs									$ 62
Asset Retirement Obligation, Accretion Expense	[7]			112		109
Asset Retirement Obligation, Revision of Estimate						0
Stock Issued				2		1
Capital Project [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				10		31
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			289		278
Amortization of intangible assets, net	[1]			13		11
Amortization of Power Contracts Emission Credits	[2]			2		(14)
Total depreciation, amortization and accretion				678		667
Amortization of Nuclear Fuel Lease	[3]			264		283
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				54		54
Gain (loss) on equity method investments				10		3
Provision for uncollectible accounts				9		6
Stock-based compensation costs				0		0
Other Decommissioning Related Activity	[4]			(84)		(55)
Energy-related options	[5]			(4)		(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)		(3)
Discrete impacts from EIMA				0		0
Amortization of debt costs				4		4
Merger related commitments						3
Inventory Write-down				1		1
InventoryLCMReservePeriodCharge						36
Restructuring Costs						4
Other				3		7
Total other noncash operating activities				(10)		51
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(167)		(148)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						119
Payments to Acquire Businesses, Gross				212		1
Capital Expenditures Incurred but Not yet Paid				(354)		(234)
Capitalized Costs, Asset Retirement Costs									62
Asset Retirement Obligation, Accretion Expense	[7]			110		109
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			190		170
Regulatory assets	[1]			18		19
Total depreciation, amortization and accretion				208		189
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				44		41
Gain (loss) on equity method investments				0		0
Provision for uncollectible accounts				7		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				0		0
Amortization of debt fair value adjustment				0		0
Discrete impacts from EIMA	[6]			(24)		(14)
Amortization of debt costs				1		1
Merger related commitments						0
Inventory Write-down				1		0
InventoryLCMReservePeriodCharge						0
Other				1		(6)
Total other noncash operating activities				31		32
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(49)		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				25		25
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense	[7]			0
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Contribution of Property	[8]					1
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			64		60
Regulatory assets	[1]			7		7
Total depreciation, amortization and accretion				71		67
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				7		8
Gain (loss) on equity method investments				0		0
Provision for uncollectible accounts				17		16
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		1
Merger related commitments						0
Inventory Write-down				0		0
InventoryLCMReservePeriodCharge						0
Other				(1)		(1)
Total other noncash operating activities				23		24
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(85)		(95)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0
Capital Expenditures Incurred but Not yet Paid				0		(65)
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense	[7]			0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			80		75
Regulatory assets	[1]			48		34
Total depreciation, amortization and accretion				128		109
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				16		16
Gain (loss) on equity method investments				0		0
Provision for uncollectible accounts				5		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				7		20
Amortization of debt fair value adjustment				0		0
Discrete impacts from EIMA				0		0
Amortization of debt costs				0		1
Merger related commitments						0
Inventory Write-down				0		0
InventoryLCMReservePeriodCharge						0
Other				(4)		(5)
Total other noncash operating activities				24		44
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(52)		(30)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0
Capital Expenditures Incurred but Not yet Paid				41		(4)
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense				0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			50		42
Regulatory assets	[1]			32		33
Amortization of intangible assets, net	[1]			0		0
Amortization of Power Contracts Emission Credits	[2]			0		0
Total depreciation, amortization and accretion				82		75
Amortization of Nuclear Fuel Lease	[3]			0		0
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				7	[9]	8	[9]	$ 7
Gain (loss) on equity method investments				0		0
Provision for uncollectible accounts				(5)		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		1
Amortization of rate stabilization deferral				(15)		1
Amortization of debt fair value adjustment				0		0
Discrete impacts from EIMA				0		0
Amortization of debt costs				0		0
Merger related commitments						138
Inventory Write-down				0		1
Other				(2)		(1)
Total other noncash operating activities				(15)		153
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(37)		(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				(6)		9
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense	[7]			0		0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			30		27
Regulatory assets	[1]			9		12
Amortization of intangible assets, net	[1]			0		0
Amortization of Power Contracts Emission Credits	[2]			0		0
Asset retirement obligation accretion						4
Total depreciation, amortization and accretion				39		39
Amortization of Nuclear Fuel Lease	[3]			0		0
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				3	[9]	5	[9]	4
Gain (loss) on equity method investments				0		0
Provision for uncollectible accounts				(1)		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				(6)		4
Amortization of debt fair value adjustment				0		0
Discrete impacts from EIMA				0		0
Amortization of debt costs				0		0
Merger related commitments						100
Inventory Write-down				0		1
Other				(3)		(1)
Total other noncash operating activities				(7)		118
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(23)		(8)
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		8
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense	[7]			0		0
Asset Retirement Obligation, Revision of Estimate						4
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]			21		20
Regulatory assets	[1]			14		20
Amortization of intangible assets, net	[1]			0		0
Amortization of Power Contracts Emission Credits	[2]			0		0
Asset retirement obligation accretion						2
Total depreciation, amortization and accretion				35		40
Amortization of Nuclear Fuel Lease	[3]			0		0
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				3	[9]	4	[9]	3
Gain (loss) on equity method investments				0		0
Provision for uncollectible accounts				1		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				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						120
Inventory Write-down				0		1
Other				(2)		(2)
Total other noncash operating activities				2		132
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities				(6)		(3)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0
Capital Expenditures Incurred but Not yet Paid				0		(9)
Capitalized Costs, Asset Retirement Costs									0
Asset Retirement Obligation, Accretion Expense	[7]			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
Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation		$ 9	[1]	112
Regulatory assets		5	[1]	55
Amortization of intangible assets, net		0	[1]	0
Amortization of Power Contracts Emission Credits		0	[2]	0
Total depreciation, amortization and accretion		14		167
Amortization of Nuclear Fuel Lease		0	[3]	0
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense		3		24
Gain (loss) on equity method investments				0
Provision for uncollectible accounts		(2)		(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		0		1
Amortization of rate stabilization deferral		0		(21)
Amortization of debt fair value adjustment		0		(2)
Discrete impacts from EIMA		0		0
Amortization of debt costs		0		0
Merger related commitments		358
Inventory Write-down		0		0
Restructuring Costs		52
Other		(1)		(6)
Total other noncash operating activities		410		(8)
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities		(25)		(75)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG		127
Capital Expenditures Incurred but Not yet Paid		(7)		(5)
Asset Retirement Obligation, Accretion Expense		0	[7]	$ 0
Business Combination, Contingent Consideration, Liability, Noncurrent									$ 45
Pepco Holdings LLC [Member] | Predecessor [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]							94
Regulatory assets	[1]							58
Amortization of intangible assets, net	[1]							0
Amortization of Power Contracts Emission Credits	[2]							0
Nuclear fuel	[3]							0
Total depreciation, amortization and accretion								152
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense								23
Gain (loss) on equity method investments								0
Provision for uncollectible accounts								16
Stock-based compensation costs								3
Other Decommissioning Related Activity								0
Energy-related options								0
Amortization of regulatory asset related to debt costs								1
Amortization of rate stabilization deferral								5
Amortization of debt fair value adjustment								0
Discrete impacts from EIMA								0
Amortization of debt costs								0
Inventory Write-down								1
Other								(3)
Total other noncash operating activities								46
Changes In Other Assets and Liabilities [Abstract]
Total changes in other assets and liabilities								(8)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid								11
Asset Retirement Obligation, Accretion Expense	[7]							$ 0
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 2016 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] Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

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

[9] Pepco's, DPL's, ACE's and PHISCO's pension and postretirement benefit costs for the three months ended March 31, 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.