Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended					6 Months Ended		9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Mar. 23, 2016	Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								$ 2,416		$ 2,490
Regulatory assets	[1]								355		293
Amortization of intangible assets, net	[1]								43		38
Amortization of Power Contracts Emission Credits	[2]								19		(7)
Amortization of Nuclear Fuel Lease	[3]								816		862
Asset Retirement Obligation, Accretion Expense	[4]								350		333
Total depreciation, amortization and accretion									3,999		4,009
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		$ 161		$ 161					482		458
Gain (loss) on equity method investments									26		15
Provision for uncollectible accounts									103		107
Stock-based compensation costs									76		88
Other Decommissioning Related Activity	[5]								(213)		(237)
Energy-related options	[6]								15		(20)
Amortization of regulatory asset related to debt costs									7		7
Amortization of rate stabilization deferral									(7)		62
Amortization of debt fair value adjustment									(13)		(9)
Discrete impacts from EIMA	[7]								(61)		(36)
Amortization of debt costs									57		26
Inventory Write-down									52		74
Merger related commitments									0	[8],[9]	508
Restructuring Costs									33		130
Asset Retirement Obligation, Revision of Estimate											0
InventoryLCMReservePeriodCharge											36
Other									46		15
Total other noncash operating activities									603		1,224
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(101)		(338)
Non cash Fair Value Adjustment for CENG											0
Business Combination, Contingent Consideration, Liability, Noncurrent		0							0
Payments to Acquire Businesses, Gross									208		6,896
Capitalized Costs, Asset Retirement Costs		(141)		476			$ 476		(141)		476
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									16		84
Stock Issued									5		2
Non Cash Licensing Agreement									8
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								1,010		1,297
Amortization of intangible assets, net	[1]								36		32
Amortization of Power Contracts Emission Credits	[2]								19		(7)
Amortization of Nuclear Fuel Lease	[3]								816		862
Asset Retirement Obligation, Accretion Expense	[4]								350		332
Total depreciation, amortization and accretion									2,231		2,516
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		57	[11]	54					170	[11]	163
Gain (loss) on equity method investments									26		16
Provision for uncollectible accounts									31		14
Stock-based compensation costs									0		0
Other Decommissioning Related Activity	[5]								(213)		(237)
Energy-related options	[6]								15		(20)
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									33		12
Inventory Write-down									50		70
Merger related commitments									0	[9]	3
Restructuring Costs									25		57
Asset Retirement Obligation, Revision of Estimate											0
InventoryLCMReservePeriodCharge											36
Other									4		24
Total other noncash operating activities									132		129
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									20		(289)
Non cash Fair Value Adjustment for CENG											119
Business Combination, Contingent Consideration, Liability, Noncurrent		33							33
Payments to Acquire Businesses, Gross									208		255
Capitalized Costs, Asset Retirement Costs				476			476				476
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									16		84
Stock Issued									0		0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								579		524
Regulatory assets	[1]								52		49
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		1
Total depreciation, amortization and accretion									631		574
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		44		41					131		124
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									25		31
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		3
Amortization of rate stabilization deferral									0		0
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA	[7]								(61)		(36)
Amortization of debt costs									3		(3)
Inventory Write-down									1		4
Merger related commitments									0	[9]	0
Restructuring Costs									0		0
Asset Retirement Obligation, Revision of Estimate											0
InventoryLCMReservePeriodCharge											0
Other									10		(1)
Total other noncash operating activities									112		122
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(79)		(42)
Non cash Fair Value Adjustment for CENG											0
Business Combination, Contingent Consideration, Liability, Noncurrent		0							0
Capitalized Costs, Asset Retirement Costs		0		0			0		0		0
Contribution of Property	[10]								21		157
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Stock Issued									0		0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								194		181
Regulatory assets	[1]								19		20
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									213		201
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		7		8					21		25
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									17		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		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		2
Inventory Write-down									0		0
Merger related commitments									0	[9]	0
Restructuring Costs									0		0
Asset Retirement Obligation, Revision of Estimate											0
InventoryLCMReservePeriodCharge											0
Other									(2)		(3)
Total other noncash operating activities									38		49
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(29)		(4)
Non cash Fair Value Adjustment for CENG											0
Business Combination, Contingent Consideration, Liability, Noncurrent		0							0
Capitalized Costs, Asset Retirement Costs		0		0			0		0		0
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Stock Issued									0		0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								233		223
Regulatory assets	[1]								115		84
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									0		0	[4]
Total depreciation, amortization and accretion									348		307
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		16		17					47		50
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									4		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		62
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA									0		0
Amortization of debt costs									1		3
Inventory Write-down									0		0
Merger related commitments									0	[9]	0
Restructuring Costs									0		0
Asset Retirement Obligation, Revision of Estimate											0
InventoryLCMReservePeriodCharge											0
Other									(7)		(18)
Total other noncash operating activities									52		109
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									16		17
Non cash Fair Value Adjustment for CENG											0
Business Combination, Contingent Consideration, Liability, Noncurrent		0							0
Capitalized Costs, Asset Retirement Costs		0		0			0		0		0
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Stock Issued									0		0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								153		128
Regulatory assets	[1]								89		93
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									242		221
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		6	[12]	8	[12]	$ 7			19	[12]	24	[12]
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									11		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		2
Amortization of rate stabilization deferral									(12)		3
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA									0		0
Amortization of debt costs									1		0
Inventory Write-down									0		1
Merger related commitments									(6)	[9]	125
Restructuring Costs									0		0
Asset Retirement Obligation, Revision of Estimate											0
InventoryLCMReservePeriodCharge											0
Other									(6)		(2)
Total other noncash operating activities									8		168
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(7)		15
Non cash Fair Value Adjustment for CENG											0
Business Combination, Contingent Consideration, Liability, Noncurrent		0							0
Noncash or Part Noncash Acquisition, Value of Liabilities Assumed											33
Capitalized Costs, Asset Retirement Costs				0			0				0
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Stock Issued									0		0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								92		82
Regulatory assets	[1]								32		38
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									124		120
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3	[12]	4	[12]	4			10	[12]	13	[12]
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									1		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									1		0
Amortization of rate stabilization deferral									(2)		3
Amortization of debt fair value adjustment									0		0
Discrete impacts from EIMA									0		0
Amortization of debt costs									0		0
Inventory Write-down									1		1
Merger related commitments									(2)	[9]	73
Restructuring Costs									0		0
Asset Retirement Obligation, Revision of Estimate											5
InventoryLCMReservePeriodCharge											0
Other									(3)		(8)
Total other noncash operating activities									6		99
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									14		(10)
Non cash Fair Value Adjustment for CENG											0
Business Combination, Contingent Consideration, Liability, Noncurrent		0							0
Capitalized Costs, Asset Retirement Costs				0			0				0
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Stock Issued									0		0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]								66		61
Regulatory assets	[1]								47		69
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									113		130
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3	[12]	4	[12]	3			10	[12]	11	[12]
Gain (loss) on equity method investments									0		0
Provision for uncollectible accounts									14		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									1		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									0		0
Inventory Write-down									0		1
Merger related commitments									0	[9]	110
Restructuring Costs									0		0
Asset Retirement Obligation, Revision of Estimate											2
InventoryLCMReservePeriodCharge											0
Other									(4)		(5)
Total other noncash operating activities									21		138
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid									(18)		2
Non cash Fair Value Adjustment for CENG											0
Business Combination, Contingent Consideration, Liability, Noncurrent		0							0
Capitalized Costs, Asset Retirement Costs				0			0				0
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Stock Issued									0		0
Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation							215	[1]	342
Regulatory assets							140	[1]	169
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							355		511
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		24		28			58		72
Gain (loss) on equity method investments									0
Provision for uncollectible accounts							27		26
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		3
Amortization of rate stabilization deferral							0		(14)
Amortization of debt fair value adjustment							0		(4)
Discrete impacts from EIMA							0		0
Amortization of debt costs							0		1
Inventory Write-down							0		1
Merger related commitments							308		(8)	[9]
Restructuring Costs							53		3
Other							(7)		(14)
Total other noncash operating activities							441		66
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid							(5)		(6)
Business Combination, Contingent Consideration, Liability, Noncurrent		$ 0		$ 53			53		0		53
Noncash or Part Noncash Acquisition, Value of Liabilities Assumed							33
Contribution of Property	[10]								0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Stock Issued									$ 0		0
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)						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
Noncash or Part Noncash Acquisition, Fixed Assets Acquired											0
Stock Issued											$ 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							$ 129

[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] See Note 12— Income Taxes for discussion of the like-kind exchange tax position

[11] FitzPatrick net benefit costs are included for the period after acquisition.

[12] Pepco's, DPL's, ACE's and PHISCO's pension and postretirement benefit costs for the nine months ended September 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.