Variable Interest Entities - Assets and Liabilities of Consolidated VIES (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,908	$ 663	$ 1,457	$ 587
Restricted cash and cash equivalents		374	438	414	358
Accounts receivable, net
Customer		3,575	3,231
Unamortized energy contract assets		38	38
Inventory, net
Materials and supplies		1,427	1,425
Assets held for sale		11	958
Other current assets		1,687	1,609
Total current assets		12,997	12,562
Property, plant and equipment, net		82,588	82,584
NDT funds		14,688	14,464
Unamortized energy contract assets		285	294
Other Assets, Noncurrent		3,033	2,982
Total assets	[1]	130,000	129,317
Long-term debt due within one year		2,281	1,819
Accounts payable		3,430	3,562
Accrued expenses		1,729	2,078
Unamortized energy contract liabilities		98	100
Liabilities held for sale		3	375
Other		1,176	1,264
Total current liabilities		13,580	12,771
Long-term debt		36,248	35,093
Asset retirement obligations, noncurrent		12,405	12,300
Unamortized energy contract liabilities		217	238
Other		2,988	2,942
Total liabilities	[1]	95,687	94,449
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		175	98
Restricted cash and cash equivalents		37	47
Accounts receivable, net
Customer		145	148
Other		35	36
Unamortized energy contract assets		22	22
Inventory, net
Materials and supplies		242	244
Assets held for sale		0	101
Other current assets		448	674
Total current assets		1,104	1,370
Property, plant and equipment, net		5,747	5,803
NDT funds		3,089	3,007
Unamortized energy contract assets		243	249
Other Assets, Noncurrent		47	52
Total noncurrent assets		9,126	9,111
Total assets		10,230	10,481
Long-term debt due within one year		90	94
Accounts payable		95	81
Accrued expenses		67	70
Unamortized energy contract liabilities		3	4
Liabilities held for sale		0	16
Other		1	5
Total current liabilities		256	270
Long-term debt		861	889
Asset retirement obligations, noncurrent		2,347	2,318
Other		116	129
Total noncurrent liabilities		3,324	3,336
Total liabilities		3,580	3,606
PP&E - unrestricted asset		1	1
Other Assets		0	9
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Inventory, net
Unamortized energy contract assets		222
Recourse [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Inventory, net
Total liabilities		2	8
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		721	226	821	303
Restricted cash and cash equivalents		41	89	150	146
Accounts receivable, net
Customer		1,792	1,298
Unamortized energy contract assets		38	38
Inventory, net
Materials and supplies		973	978
Assets held for sale		11	958
Other current assets		1,290	1,357
Total current assets		6,740	6,947
Property, plant and equipment, net		21,311	22,214
NDT funds		14,688	14,464
Unamortized energy contract assets		285	293
Other Assets, Noncurrent		1,835	1,826
Total assets	[2]	47,326	48,094
Long-term debt due within one year		699	197
Accounts payable		1,529	1,253
Accrued expenses		692	788
Unamortized energy contract liabilities		5	7
Liabilities held for sale		3	375
Other		371	444
Total current liabilities		6,298	5,219
Long-term debt		5,038	5,566
Asset retirement obligations, noncurrent		12,157	12,054
Unamortized energy contract liabilities		3	3
Other		1,405	1,308
Total liabilities	[2]	33,886	33,418
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		175	98
Restricted cash and cash equivalents		33	44
Accounts receivable, net
Customer		145	148
Other		35	36
Unamortized energy contract assets		22	22
Inventory, net
Materials and supplies		242	244
Assets held for sale		0	101
Other current assets		443	669
Total current assets		1,095	1,362
Property, plant and equipment, net		5,747	5,803
NDT funds		3,089	3,007
Unamortized energy contract assets		243	249
Other Assets, Noncurrent		38	42
Total noncurrent assets		9,117	9,101
Total assets		10,212	10,463
Long-term debt due within one year		69	68
Accounts payable		95	81
Accrued expenses		67	70
Unamortized energy contract liabilities		3	4
Liabilities held for sale		0	16
Other		1	5
Total current liabilities		235	244
Long-term debt		861	889
Asset retirement obligations, noncurrent		2,347	2,318
Other		116	129
Total noncurrent liabilities		3,324	3,336
Total liabilities		3,559	3,580
PP&E - unrestricted asset		1	1
Other Assets		0	9
Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Inventory, net
Unamortized energy contract assets		222
Exelon Generation Co L L C [Member] | Recourse [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Inventory, net
Total liabilities		2	8
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		558	111	49	131
Restricted cash and cash equivalents		37	39	37	36
Accounts receivable, net
Customer		456	525
Inventory, net
Materials and supplies		196	198
Other current assets		52	45
Total current assets		1,976	1,599
Property, plant and equipment, net		15,651	15,377
Other Assets, Noncurrent		310	307
Total assets	[3]	24,387	23,736
Long-term debt due within one year		304	347
Accounts payable		503	539
Accrued expenses		279	299
Unamortized energy contract liabilities		92	92
Other		137	141
Total current liabilities		1,643	2,154
Long-term debt		7,273	6,659
Asset retirement obligations, noncurrent		59	59
Unamortized energy contract liabilities		214	235
Other		595	622
Total liabilities	[3]	13,736	13,692
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash and cash equivalents		4	3
Accounts receivable, net
Customer		0	0
Other		0	0
Unamortized energy contract assets		0	0
Inventory, net
Materials and supplies		0	0
Assets held for sale		0	0
Other current assets		5	5
Total current assets		9	8
Property, plant and equipment, net		0	0
NDT funds		0	0
Unamortized energy contract assets		0	0
Other Assets, Noncurrent		9	10
Total noncurrent assets		9	10
Total assets		18	18
Long-term debt due within one year		21	26
Accounts payable		0	0
Accrued expenses		0	0
Unamortized energy contract liabilities		0	0
Liabilities held for sale		0	0
Other		0	0
Total current liabilities		21	26
Long-term debt		0	0
Asset retirement obligations, noncurrent		0	0
Other		0	0
Total noncurrent liabilities		0	0
Total liabilities		21	26
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		353	17	8	12
Restricted cash and cash equivalents		4	3	$ 3	$ 2
Accounts receivable, net
Customer		111	124
Inventory, net
Other current assets		2	3
Total current assets		631	326
Property, plant and equipment, net		3,552	3,475
Other Assets, Noncurrent		50	50
Total assets	[4]	4,679	4,286
Long-term debt due within one year		218	261
Accounts payable		162	177
Accrued expenses		48	46
Other		9	11
Total current liabilities		526	780
Long-term debt		1,500	1,152
Other		48	48
Total liabilities	[4]	2,985	2,895
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash and cash equivalents		4	3
Accounts receivable, net
Customer		0	0
Other		0	0
Unamortized energy contract assets		0	0
Inventory, net
Materials and supplies		0	0
Assets held for sale		0	0
Other current assets		0	0
Total current assets		4	3
Property, plant and equipment, net		0	0
NDT funds		0	0
Unamortized energy contract assets		0	0
Other Assets, Noncurrent		9	10
Total noncurrent assets		9	10
Total assets		13	13
Long-term debt due within one year		16	21
Accounts payable		0	0
Accrued expenses		0	0
Unamortized energy contract liabilities		0	0
Liabilities held for sale		0	0
Other		0	0
Total current liabilities		16	21
Long-term debt		0	0
Asset retirement obligations, noncurrent		0	0
Other		0	0
Total noncurrent liabilities		0	0
Total liabilities		$ 16	$ 21

[1] Exelon’s consolidated assets include $9,985 million and $10,200 million at March 31, 2021 and December 31, 2020, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,578 million and $3,598 million at March 31, 2021 and December 31, 2020, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 16 — Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $9,967 million and $10,182 million at March 31, 2021 and December 31, 2020, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,557 million and $3,572 million at March 31, 2021 and December 31, 2020, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 16 — Variable Interest Entities for additional information.

[3] PHI’s consolidated total assets include $18 million at both March 31, 2021 and December 31, 2020 of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $21 million and $26 million at March 31, 2021 and December 31, 2020, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 16 — Variable Interest Entities for additional information.

[4] ACE’s consolidated total assets include $13 million at both March 31, 2021 and December 31, 2020, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $16 million and $21 million at March 31, 2021 and December 31, 2020, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 16 — Variable Interest Entities for additional information.