Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended							6 Months Ended
		Jun. 30, 2017		Jun. 30, 2016		Jun. 30, 2016		Mar. 23, 2016	Jun. 30, 2017		Jun. 30, 2016
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								$ 1,545		$ 1,432
Regulatory assets	[1]								238		166
Amortization of intangible assets, net	[1]								28		28
Amortization of Power Contracts Emission Credits	[2]								20		(7)
Amortization of Nuclear Fuel Lease	[3]								529		557
Asset Retirement Obligation, Accretion Expense	[4]								231		220
Total depreciation, amortization and accretion									2,591		2,396
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		$ 163		$ 160					320		297
Gain (loss) on equity method investments									19		10
Provision for uncollectible accounts									52		51
Stock-based compensation costs									57		67
Other Decommissioning Related Activity	[5]								(144)		(123)
Energy-related options	[6]								11		(17)
Amortization of regulatory asset related to debt costs									4		4
Amortization of rate stabilization deferral									(8)		34
Amortization of debt fair value adjustment									9		(6)
Discrete impacts from EIMA	[7]								(51)		(21)
Amortization of debt costs									49		14
Inventory Write-down									51		68
Merger related commitments									0	[8],[9]	503
Restructuring Costs									25		122
Asset Retirement Obligation, Revision of Estimate											0
InventoryLCMReservePeriodCharge											36
Other									39		17
Total other noncash operating activities									415		1,056
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(105)		(364)
Non cash Fair Value Adjustment for CENG											0
Payments to Acquire Businesses, Gross									212		6,642
Capitalized Costs, Asset Retirement Costs		103		471		$ 471			103		471
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									13		60
Stock Issued									3		2
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								612		674
Amortization of intangible assets, net	[1]								25		23
Amortization of Power Contracts Emission Credits	[2]								20		(7)
Amortization of Nuclear Fuel Lease	[3]								529		557
Asset Retirement Obligation, Accretion Expense	[4]								229		220
Total depreciation, amortization and accretion									1,415		1,467
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		59	[10]	55					113	[10]	109
Gain (loss) on equity method investments									19		11
Provision for uncollectible accounts									19		13
Stock-based compensation costs									0		0
Other Decommissioning Related Activity	[5]								(144)		(123)
Energy-related options	[6]								11		(17)
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									30		10
Inventory Write-down									49		66
Merger related commitments									0	[9]	3
Restructuring Costs									17		50
InventoryLCMReservePeriodCharge											36
Other									13		17
Total other noncash operating activities									121		169
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									48		(317)
Non cash Fair Value Adjustment for CENG											119
Payments to Acquire Businesses, Gross									212		1
Capitalized Costs, Asset Retirement Costs				471		471					471
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									13		60
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								384		345
Regulatory assets	[1]								35		34
Amortization of intangible assets, net	[1]								0
Amortization of Power Contracts Emission Credits	[2]								0
Amortization of Nuclear Fuel Lease	[3]								0
Asset Retirement Obligation, Accretion Expense	[4]								0
Total depreciation, amortization and accretion									419		379
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		44		42					87		83
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									15		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									2		2
Amortization of rate stabilization deferral									0		0
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA	[7]								(51)		(21)
Amortization of debt costs									2		2
Inventory Write-down									1		2
Merger related commitments											0
InventoryLCMReservePeriodCharge											0
Other									2		(3)
Total other noncash operating activities									58		83
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(82)		(21)
Non cash Fair Value Adjustment for CENG											0
Capitalized Costs, Asset Retirement Costs		0		0		0			0		0
Contribution of Property	[11]								23		5
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								129		121
Regulatory assets	[1]								12		13
Amortization of intangible assets, net	[1]								0
Amortization of Power Contracts Emission Credits	[2]								0
Amortization of Nuclear Fuel Lease	[3]								0
Asset Retirement Obligation, Accretion Expense	[4]								0
Total depreciation, amortization and accretion									141		134
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		7		8					14		17
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									9		10
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
Merger related commitments											0
InventoryLCMReservePeriodCharge											0
Other									(2)		(2)
Total other noncash operating activities									22		27
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(44)		(12)
Non cash Fair Value Adjustment for CENG											0
Capitalized Costs, Asset Retirement Costs		0		0		0			0		0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								155		150
Regulatory assets	[1]								84		56
Amortization of intangible assets, net	[1]								0
Amortization of Power Contracts Emission Credits	[2]								0
Amortization of Nuclear Fuel Lease	[3]								0
Asset Retirement Obligation, Accretion Expense									0
Total depreciation, amortization and accretion									239		206
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		16		18					31		33
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									3		3
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		34
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA									0		0
Amortization of debt costs									1		2
Inventory Write-down									0		0
Merger related commitments											0
InventoryLCMReservePeriodCharge											0
Other									(7)		(12)
Total other noncash operating activities									35		60
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									6		2
Non cash Fair Value Adjustment for CENG											0
Capitalized Costs, Asset Retirement Costs		0		0		0			0		0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								101		85
Regulatory assets	[1]								59		59
Amortization of intangible assets, net	[1]								0		0
Amortization of Power Contracts Emission Credits	[2]								0		0
Amortization of Nuclear Fuel Lease	[3]								0		0
Asset Retirement Obligation, Accretion Expense	[4]								0		0
Total depreciation, amortization and accretion									160		144
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		6	[12]	7	[12]			$ 7	13	[12]	16	[12]
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									4		8
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									(10)		(2)
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA									0		0
Amortization of debt costs									0		0
Inventory Write-down									0		1
Merger related commitments									(6)	[9]	138
Other									(2)		(4)
Total other noncash operating activities									0		158
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									0		11
Non cash Fair Value Adjustment for CENG											0
Payments to Acquire Businesses, Gross											33
Capitalized Costs, Asset Retirement Costs				0		0					0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								61		55
Regulatory assets	[1]								18		21
Amortization of intangible assets, net	[1]								0		0
Amortization of Power Contracts Emission Credits	[2]								0		0
Amortization of Nuclear Fuel Lease	[3]								0		0
Asset Retirement Obligation, Accretion Expense	[4]								0		0
Total depreciation, amortization and accretion									79		76
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3	[12]	4	[12]			4	6	[12]	9	[12]
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									0		8
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									(5)		2
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA									0		0
Amortization of debt costs									0		0
Inventory Write-down									0		1
Merger related commitments									(2)	[9]	100
Asset Retirement Obligation, Revision of Estimate											4
Other									(3)		(3)
Total other noncash operating activities									(3)		121
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									15		(9)
Non cash Fair Value Adjustment for CENG											0
Capitalized Costs, Asset Retirement Costs				0		0					0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								44		40
Regulatory assets	[1]								28		41
Amortization of intangible assets, net	[1]								0		0
Amortization of Power Contracts Emission Credits	[2]								0		0
Amortization of Nuclear Fuel Lease	[3]								0		0
Asset Retirement Obligation, Accretion Expense	[4]								0		0
Total depreciation, amortization and accretion									72		81
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3	[12]	4	[12]			3	7	[12]	8	[12]
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									2		10
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
Inventory Write-down									0		1
Merger related commitments									0	[9]	120
Asset Retirement Obligation, Revision of Estimate											2
Other									(2)		(3)
Total other noncash operating activities									7		138
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(14)		6
Non cash Fair Value Adjustment for CENG											0
Capitalized Costs, Asset Retirement Costs				0		0					0
Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation						111	[1]		227
Regulatory assets						63	[1]		105
Amortization of intangible assets, net						0	[1]		0
Amortization of Power Contracts Emission Credits						0	[2]		0
Amortization of Nuclear Fuel Lease						0	[3]		0
Asset Retirement Obligation, Accretion Expense						0	[4]		0
Total depreciation, amortization and accretion						174			332
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		24				31			48
Gain (loss) on equity method investments									0
Provision for uncollectible accounts						7			6
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			(15)
Amortization of debt fair value adjustment						0			3
Discrete impacts from EIMA						0			0
Amortization of debt costs						0			0
Inventory Write-down						0			1
Merger related commitments						358			(8)	[9]
Restructuring Costs						54			3
Other						(7)			(6)
Total other noncash operating activities						444			28
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						(4)			(8)
Business Combination, Contingent Consideration, Liability, Noncurrent		$ 0		53		53			$ 0		$ 53
Payments to Acquire Businesses, Gross						33
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
Amortization of Nuclear Fuel Lease	[3]							0
Asset Retirement Obligation, Accretion Expense	[4]							0
Total depreciation, amortization and accretion								152
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)				$ 27		31		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
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid								11
Non cash Fair Value Adjustment for CENG								$ 0
Pepco Holdings LLC [Member] | Deferred Compensation, Share-based Payments [Member] | Successor [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Payments to Acquire Businesses, Gross						29
Pepco Holdings LLC [Member] | Fair Value Measurement [Domain] | Successor [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						$ 127

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

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

[5] 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

[6] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded in Operating revenues.

[7] Reflects the change in distribution rates pursuant to EIMA and FEJA, which allows for the recovery of distribution costs by a utility through a pre-established performance-based formula rate tariff. Beginning June 1, 2017, also reflects the change in energy efficiency rates pursuant to FEJA, which allows for the recovery of energy efficiency costs by a utility through a pre-established performance-based formula rate tariff. See Note 5 — Regulatory Matters for more information

[8] 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.

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

[10] (c)FitzPatrick net benefit costs are included for the period after acquisition.

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

[12] 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.