Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Depreciation, amortization and accretion
Depreciation	$ 4,364	$ 3,665	$ 3,740
Amortization of Regulatory Asset	588	528	555
Amortization of Intangible Assets	(17)	(28)	(109)
Amortization of Nuclear Fuel Lease	983	1,016	1,115
Accretion expense	500	491	489
Total depreciation, amortization and accretion	6,527	5,780	5,971
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	1,521	1,470	1,421
Income taxes (net of refunds)	10	265	95
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	411	438	583
Provision for uncollectible accounts	150	120	159
Other decommissioning related-activity	(659)	(506)	(2)
Energy-related options	104	22	10
True-up Adjustments to Decoupling Mechanisms and Formula Rate	(6)	124	49
Restructuring Costs	105
Inventory Write-down	131
Asset Retirement Obligation, Revision of Estimate			20
Long-term incentive plan	56	10	140
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	222	244
Change in environmental liabilities		23
Asset impairments	591	201	50
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(104)	(85)	(69)
Other Non- Cash
Other non-cash operating activities:
Asset impairments	0
Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(104)	(85)	(69)
Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Depreciation	2,070	1,485	1,748
Amortization of Regulatory Asset	0	0	0
Amortization of Intangible Assets	81	74	63
Amortization of Nuclear Fuel Lease	983	1,016	1,115
Accretion expense	500	491	489
Total depreciation, amortization and accretion	3,636	3,063	3,415
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	331	373	369
Income taxes (net of refunds)	70	(44)	746
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	115	135	204
Provision for uncollectible accounts	17	31	48
Other decommissioning related-activity	(659)	(506)	(2)
Energy-related options	104	22	10
True-up Adjustments to Decoupling Mechanisms and Formula Rate	0	0	0
Restructuring Costs	90
Inventory Write-down	128
Asset Retirement Obligation, Revision of Estimate			0
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	155	172
Change in environmental liabilities		0
Asset impairments	563	201	50
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	0	0	0
Exelon Generation Co L L C [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	0
Exelon Generation Co L L C [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	0	0	0
Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Depreciation	922	886	820
Amortization of Regulatory Asset	211	147	120
Amortization of Intangible Assets	7	7	7
Amortization of Nuclear Fuel Lease	0	0	0
Accretion expense	0	0	0
Total depreciation, amortization and accretion	1,133	1,033	940
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	371	343	332
Income taxes (net of refunds)	(61)	(42)	(153)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	114	96	177
Provision for uncollectible accounts	32	33	40
Other decommissioning related-activity	0	0	0
Energy-related options	0	0	0
True-up Adjustments to Decoupling Mechanisms and Formula Rate	47	128	28
Restructuring Costs	1
Inventory Write-down	2
Asset Retirement Obligation, Revision of Estimate			0
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	2	3
Change in environmental liabilities		0
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(29)	(17)	(19)
Commonwealth Edison Co [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	15
Commonwealth Edison Co [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(29)	(17)	(19)
PECO Energy Co [Member]
Depreciation, amortization and accretion
Depreciation	319	303	274
Amortization of Regulatory Asset	28	30	27
Amortization of Nuclear Fuel Lease	0	0	0
Accretion expense	0	0	0
Total depreciation, amortization and accretion	347	333	301
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	144	129	125
Income taxes (net of refunds)	(37)	82	(2)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	5	12	18
Provision for uncollectible accounts	42	31	33
Other decommissioning related-activity	0	0	0
Energy-related options	0	0	0
True-up Adjustments to Decoupling Mechanisms and Formula Rate	(16)	0	0
Restructuring Costs	1
Inventory Write-down	1
Asset Retirement Obligation, Revision of Estimate			0
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	1	0
Change in environmental liabilities		0
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(17)	(13)	(7)
PECO Energy Co [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	0
PECO Energy Co [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(17)	(13)	(7)
Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Depreciation	397	359	335
Amortization of Regulatory Asset	153	143	148
Amortization of Nuclear Fuel Lease	0	0	0
Accretion expense	0	0	0
Total depreciation, amortization and accretion	550	502	483
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	125	106	94
Income taxes (net of refunds)	(57)	17	14
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	62	61	59
Provision for uncollectible accounts	15	8	10
Other decommissioning related-activity	0	0	0
Energy-related options	0	0	0
True-up Adjustments to Decoupling Mechanisms and Formula Rate	(16)	0	0
Restructuring Costs	0
Inventory Write-down	0
Asset Retirement Obligation, Revision of Estimate			0
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	31	30
Change in environmental liabilities		0
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(22)	(21)	(18)
Baltimore Gas and Electric Company [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	0
Baltimore Gas and Electric Company [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(22)	(21)	(18)
Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Depreciation	586	547	480
Amortization of Regulatory Asset	196	207	260
Amortization of Intangible Assets	(115)	(119)	(188)
Amortization of Nuclear Fuel Lease	0	0	0
Accretion expense	0	0	0
Total depreciation, amortization and accretion	782	754	740
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	257	255	250
Income taxes (net of refunds)	46	29	(32)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	70	95	67
Provision for uncollectible accounts	43	17	28
Other decommissioning related-activity	0	0	0
Energy-related options	0	0	0
True-up Adjustments to Decoupling Mechanisms and Formula Rate	(21)	(4)	21
Restructuring Costs	0
Inventory Write-down	0
Asset Retirement Obligation, Revision of Estimate			20
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	28	33
Change in environmental liabilities		23
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(36)	(34)	(25)
Pepco Holdings LLC [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	13
Pepco Holdings LLC [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(36)	(34)	(25)
Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Depreciation	257	239	218
Amortization of Regulatory Asset	120	135	167
Amortization of Nuclear Fuel Lease	0	0	0
Accretion expense	0	0	0
Total depreciation, amortization and accretion	377	374	385
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	129	130	123
Income taxes (net of refunds)	40	7	41
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	15	25	15
Provision for uncollectible accounts	24	7	11
Other decommissioning related-activity	0	0	0
Energy-related options	0	0	0
True-up Adjustments to Decoupling Mechanisms and Formula Rate	(40)	(4)	21
Restructuring Costs	0
Inventory Write-down	0
Asset Retirement Obligation, Revision of Estimate			22
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	7	8
Change in environmental liabilities		23
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(28)	(25)	(22)
Potomac Electric Power Company [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	0
Potomac Electric Power Company [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(28)	(25)	(22)
Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Depreciation	155	146	131
Amortization of Regulatory Asset	36	38	51
Amortization of Nuclear Fuel Lease	0	0	0
Accretion expense	0	0	0
Total depreciation, amortization and accretion	191	184	182
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	61	59	56
Income taxes (net of refunds)	12	19	(6)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	7	15	6
Provision for uncollectible accounts	16	4	6
Other decommissioning related-activity	0	0	0
Energy-related options	0	0	0
True-up Adjustments to Decoupling Mechanisms and Formula Rate	7	0	0
Restructuring Costs	0
Inventory Write-down	0
Asset Retirement Obligation, Revision of Estimate			(1)
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	8	8
Change in environmental liabilities		0
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(4)	(4)	(2)
Delmarva Power & Light Company [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	7
Delmarva Power & Light Company [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(4)	(4)	(2)
Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Depreciation	140	123	94
Amortization of Regulatory Asset	40	34	42
Amortization of Nuclear Fuel Lease	0	0	0
Accretion expense	0	0	0
Total depreciation, amortization and accretion	180	157	136
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	57	55	61
Income taxes (net of refunds)	(3)	(5)	(12)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	14	16	12
Provision for uncollectible accounts	2	5	11
Other decommissioning related-activity	0	0	0
Energy-related options	0	0	0
True-up Adjustments to Decoupling Mechanisms and Formula Rate	12	0	0
Restructuring Costs	0
Inventory Write-down	0
Asset Retirement Obligation, Revision of Estimate			(1)
Long-term incentive plan	0	0	0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	3	4
Change in environmental liabilities		0
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(4)	(5)	(1)
Atlantic City Electric Company [Member] \| Other Non- Cash
Other non-cash operating activities:
Asset impairments	6
Atlantic City Electric Company [Member] \| Return on borrowed funds
Other non-cash operating activities:
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	(4)	(5)	(1)
Other Intangible Assets [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	62	59	58
Other Intangible Assets [Member] \| Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	53	50	49
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	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	30	21	14
Unamortized Energy Contracts [Member] \| Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	30	21	14
Unamortized Energy Contracts [Member] \| Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	0	0	0
Unamortized Energy Contracts [Member] \| PECO Energy Co [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	0	0	0
Unamortized Energy Contracts [Member] \| Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	0	0	0
Unamortized Energy Contracts [Member] \| Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	0	0	0
Unamortized Energy Contracts [Member] \| Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	0	0	0
Unamortized Energy Contracts [Member] \| Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	0	0	0
Unamortized Energy Contracts [Member] \| Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	$ 0	$ 0	$ 0

Cash Paid (Refunded) During the Year

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Represents the reclassification of energy-related option premiums to realized at settlement of contracts recorded in results of operations due to the settlement of the underlying transaction.

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This item represents realized and unrealized gains (losses) for the period as a result of selling and holding marketable securities in nuclear decommissioning trust funds. Additionally, this item includes the elimination of operating revenues, asset retirement obligation accretion, asset retirement cost amortization, investment income and income taxes related to nuclear decommissioning trust fund activity. As a result of certain regulatory agreements for these nuclear decommissioning trust funds; upon completion of decommissioning activities, excess (shortfall of) funds will be refunded to (recovered from) rate payers through a regulated affiliate. Therefore, this activity is contractually eliminated within the income statement.

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True-up Adjustments to Decoupling Mechanisms and Formula Rate

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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The expense charged against earnings for the periodic recognition of capitalized nuclear fuel leases.

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The expense charged against earnings for the periodic recognition of capitalized costs related to purchasing power, fuel, or emission credits. These items may be purchased in one accounting period but are deducted from earnings over time through amortization.

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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The aggregate net amount of depreciation, amortization, and accretion recognized during an accounting period. As a noncash item, the net amount is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Amount of noncash expense (reversal of expense) for employee benefits and share-based payment arrangement. Includes, but is not limited to, pension, other postretirement, postemployment and termination benefits.

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The adjustment to exclude the noncash portion of, and include cash payments for environmental costs when calculating operating cash flows under the indirect method. The adjustment can include the increase (decrease) during an accounting period in total estimated obligations recorded for probable future loss attributable to environmental contamination issues.

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

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Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

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Amount of loss from reductions in inventory due to subsequent measurement adjustments, including, but not limited to, physical deterioration, obsolescence, or changes in price levels.

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The total depreciation charge recorded for property subject to or held for lease.

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Amount of cost (reversal of cost) for pension and other postretirement benefits.

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Amount of expense (reversal of expense) for expected credit loss on accounts receivable.

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The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

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Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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