Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Depreciation, amortization and accretion
Depreciation	$ 3,665	$ 3,740	$ 3,293
Amortization of Regulatory Asset	528	555	478
Amortization of Intangible Assets	(28)	(109)	(237)
Amortization of Nuclear Fuel Lease	1,016	1,115	1,096
Accretion expense	491	489	468
Total depreciation, amortization and accretion	5,780	5,971	5,427
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	1,470	1,421	2,430
Income taxes (net of refunds)	265	95	540
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	438	583	643
Provision for uncollectible accounts	120	159	125
Other decommissioning related-activity	(506)	(2)	(313)
Energy-related options	22	10	7
Amortization of rate stabilization deferral	(4)	21	(3)
Asset Retirement Obligation, Revision of Estimate		20
Discrete impacts from EIMA and FEJA	128	28	(52)
Vacation accrual adjustment		68	(68)
Long-term incentive plan	10	140	109
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	244
Change in environmental liabilities	23		44
Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Depreciation	1,485	1,748	1,409
Amortization of Regulatory Asset	0	0	0
Amortization of Intangible Assets	74	63	83
Amortization of Nuclear Fuel Lease	1,016	1,115	1,096
Accretion expense	491	489	468
Total depreciation, amortization and accretion	3,063	3,415	3,056
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	373	369	391
Income taxes (net of refunds)	(44)	746	337
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	135	204	227
Provision for uncollectible accounts	31	48	38
Other decommissioning related-activity	(506)	(2)	(313)
Energy-related options	22	10	7
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		0
Vacation accrual adjustment			(35)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	172
Change in environmental liabilities	0		44
Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Depreciation	886	820	777
Amortization of Regulatory Asset	147	120	73
Amortization of Intangible Assets	7	7	7
Accretion expense	0	0	0
Total depreciation, amortization and accretion	1,033	940	850
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	343	332	307
Income taxes (net of refunds)	(42)	(153)	83
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	96	177	176
Provision for uncollectible accounts	33	40	34
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		0
Discrete impacts from EIMA and FEJA	128	28	(52)
Vacation accrual adjustment			(12)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	3
Change in environmental liabilities	0		0
PECO Energy Co [Member]
Depreciation, amortization and accretion
Depreciation	303	274	261
Amortization of Regulatory Asset	30	27	25
Accretion expense	0	0	0
Total depreciation, amortization and accretion	333	301	286
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	129	125	103
Income taxes (net of refunds)	82	(2)	47
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	12	18	29
Provision for uncollectible accounts	31	33	26
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		0
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	0
Change in environmental liabilities	0		0
Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Depreciation	359	335	312
Amortization of Regulatory Asset	143	148	161
Accretion expense	0	0	0
Total depreciation, amortization and accretion	502	483	473
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	106	94	96
Income taxes (net of refunds)	17	14	(2)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	61	59	62
Provision for uncollectible accounts	8	10	8
Amortization of rate stabilization deferral	0	0	7
Asset Retirement Obligation, Revision of Estimate		0
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	30
Change in environmental liabilities	0		0
Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Depreciation	547	480	457
Amortization of Regulatory Asset	207	260	218
Amortization of Intangible Assets	(119)	(188)	(336)
Accretion expense	0	0	0
Total depreciation, amortization and accretion	754	740	675
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	255	250	236
Income taxes (net of refunds)	29	(32)	(144)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	95	67	94
Provision for uncollectible accounts	17	28	19
Amortization of rate stabilization deferral	(4)	21	(10)
Asset Retirement Obligation, Revision of Estimate		20
Vacation accrual adjustment			(8)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	33
Change in environmental liabilities	23		0
Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Depreciation	239	218	203
Amortization of Regulatory Asset	135	167	118
Accretion expense	0	0	0
Total depreciation, amortization and accretion	374	385	321
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	130	123	114
Income taxes (net of refunds)	7	41	(104)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	25	15	25
Provision for uncollectible accounts	7	11	8
Amortization of rate stabilization deferral	(4)	21	(10)
Asset Retirement Obligation, Revision of Estimate		22
Vacation accrual adjustment			(8)
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	8
Change in environmental liabilities	23		0
Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Depreciation	146	131	124
Amortization of Regulatory Asset	38	51	43
Accretion expense	0	0	0
Total depreciation, amortization and accretion	184	182	167
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	59	56	49
Income taxes (net of refunds)	19	(6)	(49)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	15	6	13
Provision for uncollectible accounts	4	6	3
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		(1)
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	8
Change in environmental liabilities	0		0
Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Depreciation	123	94	89
Amortization of Regulatory Asset	34	42	57
Accretion expense	0	0	0
Total depreciation, amortization and accretion	157	136	146
Cash paid (refunded) during the year:
Interest (net of amount capitalized)	55	61	59
Income taxes (net of refunds)	(5)	(12)	(2)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs	16	12	13
Provision for uncollectible accounts	5	11	8
Amortization of rate stabilization deferral	0	0	0
Asset Retirement Obligation, Revision of Estimate		(1)
Vacation accrual adjustment			0
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	4
Change in environmental liabilities	0		0
Other Intangible Assets [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	59	58	57
Other Intangible Assets [Member] | Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets	50	49	48
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	21	14	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