Supplemental Financial Information Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended		12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Mar. 23, 2016	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Depreciation, amortization and accretion
Depreciation							$ 3,740		$ 3,293		$ 3,477
Amortization of Regulatory Asset							555		478		407
Amortization of Intangible Assets							(109)		(237)		(336)
Amortization of Nuclear Fuel Lease	[1]						1,115		1,096		1,159
Asset Retirement Obligation, Accretion Expense	[2]						489		468		446
Total depreciation, amortization and accretion							5,971		5,427		5,576
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							1,421		2,430		1,340
Income taxes (net of refunds)							95		540		(441)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							583		643		619
Gain (loss) on equity method investments							28		32		24
Provision for uncollectible accounts							159		125		155
Provision for excess and obsolete inventory							24		56		12
Stock-based compensation costs							75		88		111
Other decommissioning related-activity							(2)	[3]	(313)	[4]	(384)	[5]
Energy-related options							10	[6]	7	[7]	(11)	[8]
Amortization of regulatory asset related to debt costs							8		9		9
Amortization of rate stabilization deferral							14		(10)		76
Amortization of debt fair value adjustment							(15)		(18)		(11)
Merger-related commitments							0	[9]	0	[10]	558	[11],[12]
Severance costs							35		35		99
Amortization of debt costs							36		64		35
Discrete impacts from EIMA and FEJA							28	[13]	(52)	[14]	8	[15]
Vacation accrual adjustment	[16]								68
Long-term incentive plan							140		109		70
Change in environmental liabilities									44
Lower of cost or market inventory adjustment											37
Baltimore City conduit lease settlement											(28)
Cash Working Capital order											(13)
Asset Retirement Obligation, Revision of Estimate							20				2
Other							(19)		(30)		(35)
Total other non-cash operating activities							1,124		721		1,333
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							(69)		42		(128)
Change in PPE related to ARO update		$ (107)				$ 191	(107)		29		191
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									16		95
Noncash or Part Noncash Divestiture, Amount of Consideration Received	[12]										37
Dividends on stock compensation							6		7		6
Acquisition of land							3
Assumption of member purchase liability							154		208		6,923
Dissolution of financing trust due to long-term debt retirement									8
Fair value adjustment of long-term debt due to retirement									(5)
Allowance for Doubtful Accounts Receivable, Write-offs											5
Fitzpatrick [Member]
Non-cash investing and financing activities:
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[17]										(54)
Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Depreciation							1,748		1,409		1,835
Amortization of Regulatory Asset							0		0		0
Amortization of Intangible Assets							63		83		79
Amortization of Nuclear Fuel Lease	[1]						1,115		1,096		1,159
Asset Retirement Obligation, Accretion Expense	[2]						489		468		446
Total depreciation, amortization and accretion							3,415		3,056		3,519
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							369		391		339
Income taxes (net of refunds)							746		337		435
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							204		227		218
Gain (loss) on equity method investments							30		33		25
Provision for uncollectible accounts							48		38		19
Provision for excess and obsolete inventory							20		51		6
Other decommissioning related-activity							(2)	[3]	(313)	[4]	(384)	[5]
Energy-related options							10	[6]	7	[7]	(11)	[8]
Amortization of regulatory asset related to debt costs							0		0		0
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							(12)		(12)		(11)
Merger-related commitments							0	[9]	0	[10]	53	[11],[12]
Severance costs							9		31		22
Amortization of debt costs							14		37		17
Vacation accrual adjustment	[16]								35
Change in environmental liabilities									44
Lower of cost or market inventory adjustment											36
Asset Retirement Obligation, Revision of Estimate		203	$ 84		$ 138		0				0
Other							(23)		4		25
Total other non-cash operating activities							298		112		15
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							(199)		73		50
Change in PPE related to ARO update		(130)				191	(130)		29		191
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									16		95
Noncash or Part Noncash Divestiture, Amount of Consideration Received	[12]										37
Acquisition of land							0
Assumption of member purchase liability							154		208		293
Fair value of pension and OPEB obligation transferred in connection with FitzPatrick									33
Exelon Generation Co L L C [Member] | noncash member [Member]
Non-cash investing and financing activities:
Fair value of net assets contributed (distributed) in connection with the PHI merger, net of cash											119
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Non-cash investing and financing activities:
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[17]										(54)
Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Depreciation							820		777		708
Amortization of Regulatory Asset							120		73		67
Amortization of Intangible Assets							7		7		7
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							940		850		775
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							332		307		298
Income taxes (net of refunds)							(153)		83		(444)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							177		176		166
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							40		34		41
Provision for excess and obsolete inventory							3		3		4
Amortization of regulatory asset related to debt costs							3		4		4
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	0	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							5		5		4
Discrete impacts from EIMA and FEJA							28	[13]	(52)	[14]	8	[15]
Vacation accrual adjustment	[16]								12
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							0				0
Other							(14)		6		(12)
Total other non-cash operating activities							242		164		215
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							11		(61)		(91)
Change in PPE related to ARO update		7				0	7		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Contribution of Property									21	[18]	158	[19]
Acquisition of land							0
PECO Energy Co [Member]
Depreciation, amortization and accretion
Depreciation							274		261		244
Amortization of Regulatory Asset							27		25		26
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							301		286		270
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							125		103		104
Income taxes (net of refunds)							(2)		47		64
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							18		29		33
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							33		26		30
Provision for excess and obsolete inventory							0		0		0
Amortization of regulatory asset related to debt costs							1		1		1
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	0	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							2		2		3
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											1
Asset Retirement Obligation, Revision of Estimate							0				0
Other							(3)		(4)		(3)
Total other non-cash operating activities							51		54		65
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							(12)		22		(11)
Change in PPE related to ARO update		0				0	0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Depreciation							335		312		299
Amortization of Regulatory Asset							148		161		124
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							483		473		423
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							94		96		92
Income taxes (net of refunds)							14		(2)		31
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							59		62		67
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							10		8		1
Provision for excess and obsolete inventory							0		0		0
Amortization of regulatory asset related to debt costs							0		0		0
Amortization of rate stabilization deferral							0		7		81
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	0	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							1		2		1
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Baltimore City conduit lease settlement											(28)
Cash Working Capital order											(13)
Asset Retirement Obligation, Revision of Estimate							0				0
Other							(12)		(14)		(21)
Total other non-cash operating activities							58		65		88
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							50		23		(86)
Change in PPE related to ARO update		1				0	1		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Dissolution of financing trust due to long-term debt retirement									8
Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Depreciation							480		457
Amortization of Regulatory Asset							260		218
Asset Retirement Obligation, Accretion Expense	[2]						0		0
Total depreciation, amortization and accretion							740		675
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							250		236
Income taxes (net of refunds)							(32)		(144)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							67		94
Gain (loss) on equity method investments							(1)		(1)
Provision for uncollectible accounts							28		19
Provision for excess and obsolete inventory							0		2
Amortization of regulatory asset related to debt costs							4		4
Amortization of rate stabilization deferral							14		(17)
Amortization of debt fair value adjustment							(3)		(6)
Merger-related commitments							5	[9]	(8)	[10]
Severance costs							0		3
Amortization of debt costs							3		4
Vacation accrual adjustment	[16]								8
Change in environmental liabilities									0
Other							6		(28)
Total other non-cash operating activities							143		58
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							93		(12)
Change in PPE related to ARO update		15					15		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0
Acquisition of land							3
Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, amortization and accretion
Depreciation						325
Amortization of Regulatory Asset						190
Asset Retirement Obligation, Accretion Expense	[2]					0
Total depreciation, amortization and accretion						515
Cash paid (refunded) during the year:
Interest (net of amount capitalized)						209
Income taxes (net of refunds)						258
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs						86
Gain (loss) on equity method investments						0
Provision for uncollectible accounts						65
Provision for excess and obsolete inventory						1
Amortization of regulatory asset related to debt costs						3
Amortization of rate stabilization deferral						(5)
Amortization of debt fair value adjustment						0
Merger-related commitments	[11],[12]					317
Severance costs						56
Amortization of debt costs						1
Lower of cost or market inventory adjustment						0
Asset Retirement Obligation, Revision of Estimate						2	20
Other						(11)
Total other non-cash operating activities						515
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid						21
Change in PPE related to ARO update						0					0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						0
Fair value of net assets contributed (distributed) in connection with the PHI merger, net of cash	[12],[20]					127
Fair value of pension obligation transferred in connection with the PHI Merger, net of cash	[12],[20]					53
Pepco Holdings LLC [Member] | Successor [Member] | noncash member [Member]
Other non-cash operating activities:
Merger-related commitments						33
Non-cash investing and financing activities:
Assumption of member purchase liability						29
Pepco Holdings LLC [Member] | Predecessor [Member]
Depreciation, amortization and accretion
Depreciation				$ 94
Amortization of Regulatory Asset				58
Asset Retirement Obligation, Accretion Expense	[2]			0
Total depreciation, amortization and accretion				152
Cash paid (refunded) during the year:
Interest (net of amount capitalized)				43
Income taxes (net of refunds)				11
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs				23
Gain (loss) on equity method investments				0
Provision for uncollectible accounts				16
Provision for excess and obsolete inventory				1
Stock-based compensation costs				3
Amortization of regulatory asset related to debt costs				1
Amortization of rate stabilization deferral				5
Amortization of debt fair value adjustment				0
Merger-related commitments	[11],[12]			0
Severance costs				0
Amortization of debt costs				0
Lower of cost or market inventory adjustment				0
Asset Retirement Obligation, Revision of Estimate				0
Other				(3)
Total other non-cash operating activities				46
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid				11
Change in PPE related to ARO update				0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Depreciation							218		203		175
Amortization of Regulatory Asset							167		118		120
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							385		321		295
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							123		114		118
Income taxes (net of refunds)							41		(104)		216
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							15		25		31
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							11		8		29
Provision for excess and obsolete inventory							0		1		3
Amortization of regulatory asset related to debt costs							2		2		2
Amortization of rate stabilization deferral							14		(17)		(12)
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	(6)	[10]	125	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							2		2		0
Vacation accrual adjustment	[16]								8
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							22				0
Other							(6)		(13)		(3)
Total other non-cash operating activities							60		(6)		175
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							20		5		27
Change in PPE related to ARO update		12				0	12		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Potomac Electric Power Company [Member] | noncash member [Member]
Other non-cash operating activities:
Merger-related commitments											33
Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Depreciation							131		124		110
Amortization of Regulatory Asset							51		43		47
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							182		167		157
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							56		49		47
Income taxes (net of refunds)							(6)		(49)		115
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							6		13		18
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							6		3		23
Provision for excess and obsolete inventory							0		1		1
Amortization of regulatory asset related to debt costs							1		1		1
Amortization of rate stabilization deferral							0		0		2
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							5	[9]	(2)	[10]	82	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							0		0		0
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							(1)				1
Other							7		(7)		(14)
Total other non-cash operating activities							24		9		114
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							22		4		(12)
Change in PPE related to ARO update		2				0	2		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Depreciation							94		89		82
Amortization of Regulatory Asset							42		57		83
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							136		146		165
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							61		59		62
Income taxes (net of refunds)							(12)		(2)		200
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							12		13		15
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							11		8		32
Provision for excess and obsolete inventory							0		0		1
Amortization of regulatory asset related to debt costs							1		1		1
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	110	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							1		1		0
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							(1)				2
Other							0		(6)		(6)
Total other non-cash operating activities							24		17		155
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							46		(13)		11
Change in PPE related to ARO update		$ 1				0	1		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							3
Other Intangible Assets [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							58		57		52
Other Intangible Assets [Member] | Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							49		48		44
Other Intangible Assets [Member] | Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | PECO Energy Co [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets						$ 0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets				$ 0
Other Intangible Assets [Member] | Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Unamortized Energy Contracts [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	[21]						14		35		35
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	[21]						$ 14		$ 35		$ 35

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

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

[3] Includes the elimination of decommissioning-related activities 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 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.

[4] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246ODE3Q0FGRTQ3ODgzNTMyQkFDNzc4ODYwRDFBNDI1OTMM}

[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 15 — Asset Retirement Obligations 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 to results of operations.

[7] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.

[8] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.

[9] See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

[10] See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

[11] 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.

[12] See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

[13] Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 4 — Regulatory Matters for additional information.

[14] Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 4 — Regulatory Matters for additional information.

[15] 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. See Note 4 — Regulatory Matters for additional information.

[16] On December 1, 2017, Exelon adopted a single, standard vacation accrual policy for all non-represented, non-craft (represented and craft policies remained unchanged) employees effective January 1, 2018. To reflect the new policy, Exelon recorded a one-time, $68 million pre-tax credit to expense to reverse 2018 vacation cost originally accrued throughout 2017 that will now be accrued ratably over the year in 2018.

[17] Reflects the transfer of nuclear fuel to Entergy under the cost reimbursement provisions of the FitzPatrick acquisition agreements. See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

[18] See Note 14 — Income Taxes for additional information on the like-kind exchange tax position

[19] See Note 14 — Income Taxes for additional information on the like-kind exchange tax position.

[20] Immediately following closing of the PHI Merger, the net assets associated with PHI’s unregulated business interests were distributed by PHI to Exelon. Exelon contributed a portion of such net assets to Generation.

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