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