Variable Interest Entities - Assets and Liabilities of Consolidated VIES (Details) - USD ($) $ in Millions		Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 2,957	$ 663	$ 1,858	$ 587
Restricted cash and cash equivalents		473	438	485	358
Accounts receivable, net
Customer		3,121	3,231
Unamortized energy contract assets		36	38
Inventory, net
Materials and supplies		1,475	1,425
Assets held for sale		11	958
Other current assets		1,665	1,609
Total current assets		14,877	12,562
Property, plant and equipment, net		82,852	82,584
NDT funds		15,404	14,464
Unamortized energy contract assets		265	294
Other Assets, Noncurrent		2,818	2,982
Assets	[1]	132,621	129,317
Long-term debt due within one year		3,375	1,819
Accounts payable		3,694	3,562
Accrued expenses		1,949	2,078
Unamortized energy contract liabilities		92	100
Liabilities held for sale		3	375
Other		1,180	1,264
Total current liabilities		15,826	12,771
Long-term debt		35,269	35,093
Asset retirement obligations, noncurrent		12,907	12,300
Unamortized energy contract liabilities		169	238
Other		2,850	2,942
Total liabilities	[1]	98,362	94,449
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		38	98
Restricted cash and cash equivalents		47	47
Accounts receivable, net
Customer		25	148
Other		7	36
Unamortized energy contract assets		21	22
Inventory, net
Materials and supplies		14	244
Assets held for sale		0	101
Other current assets		517	674
Total current assets		669	1,370
Property, plant and equipment, net		2,052	5,803
NDT funds		0	3,007
Unamortized energy contract assets		210	249
Other Assets, Noncurrent		22	52
Assets, Noncurrent		2,284	9,111
Assets		2,953	10,481
Long-term debt due within one year		80	94
Accounts payable		11	81
Accrued expenses		14	70
Unamortized energy contract liabilities		0	4
Liabilities held for sale		0	16
Other		0	5
Total current liabilities		105	270
Long-term debt		832	889
Asset retirement obligations, noncurrent		149	2,318
Other		3	129
Liabilities, Noncurrent		984	3,336
Total liabilities		1,089	3,606
Unrestricted Assets [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Accounts receivable, net
Unamortized energy contract assets		21	22
Inventory, net
Assets held for sale		0	9
Unamortized energy contract assets		210	249
Other Assets		0	1
Recourse [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Inventory, net
Total liabilities		1	8
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		1,957	226	623	303
Restricted cash and cash equivalents		62	89	100	146
Accounts receivable, net
Customer		1,328	1,298
Unamortized energy contract assets		36	38
Inventory, net
Materials and supplies		998	978
Assets held for sale		11	958
Other current assets		1,319	1,357
Total current assets		8,587	6,947
Property, plant and equipment, net		19,574	22,214
NDT funds		15,404	14,464
Unamortized energy contract assets		265	293
Other Assets, Noncurrent		1,589	1,826
Assets	[2]	48,010	48,094
Long-term debt due within one year		1,216	197
Accounts payable		1,612	1,253
Accrued expenses		691	788
Unamortized energy contract liabilities		2	7
Liabilities held for sale		3	375
Other		347	444
Total current liabilities		7,796	5,219
Long-term debt		4,593	5,566
Asset retirement obligations, noncurrent		12,635	12,054
Unamortized energy contract liabilities		1	3
Other		1,224	1,308
Total liabilities	[2]	35,975	33,418
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		38	98
Restricted cash and cash equivalents		42	44
Accounts receivable, net
Customer		25	148
Other		7	36
Unamortized energy contract assets		21	22
Inventory, net
Materials and supplies		14	244
Assets held for sale		0	101
Other current assets		513	669
Total current assets		660	1,362
Property, plant and equipment, net		2,052	5,803
NDT funds		0	3,007
Unamortized energy contract assets		210	249
Other Assets, Noncurrent		13	42
Assets, Noncurrent		2,275	9,101
Assets		2,935	10,463
Long-term debt due within one year		70	68
Accounts payable		11	81
Accrued expenses		14	70
Unamortized energy contract liabilities		0	4
Liabilities held for sale		0	16
Other		0	5
Total current liabilities		95	244
Long-term debt		832	889
Asset retirement obligations, noncurrent		149	2,318
Other		3	129
Liabilities, Noncurrent		984	3,336
Total liabilities		1,079	3,580
Exelon Generation Co L L C [Member] | Unrestricted Assets [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Accounts receivable, net
Unamortized energy contract assets		21	22
Inventory, net
Assets held for sale		0	9
Unamortized energy contract assets		210	249
Other Assets		0	1
Exelon Generation Co L L C [Member] | Recourse [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Inventory, net
Total liabilities		1	8
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		82	111	196	131
Restricted cash and cash equivalents		71	39	38	36
Accounts receivable, net
Customer		566	525
Inventory, net
Materials and supplies		207	198
Other current assets		57	45
Total current assets		1,690	1,599
Property, plant and equipment, net		16,163	15,377
Other Assets, Noncurrent		283	307
Assets	[3]	24,502	23,736
Long-term debt due within one year		405	347
Accounts payable		479	539
Accrued expenses		300	299
Unamortized energy contract liabilities		90	92
Other		154	141
Total current liabilities		2,015	2,154
Long-term debt		7,077	6,659
Asset retirement obligations, noncurrent		69	59
Unamortized energy contract liabilities		168	235
Other		589	622
Total liabilities	[3]	13,861	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		5	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		4	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
Assets, Noncurrent		9	10
Assets		18	18
Long-term debt due within one year		10	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		10	26
Long-term debt		0	0
Asset retirement obligations, noncurrent		0	0
Other		0	0
Liabilities, Noncurrent		0	0
Total liabilities		10	26
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		16	17	13	12
Restricted cash and cash equivalents		5	3	$ 4	$ 2
Accounts receivable, net
Customer		184	124
Inventory, net
Other current assets		5	3
Total current assets		376	326
Property, plant and equipment, net		3,649	3,475
Other Assets, Noncurrent		48	50
Assets	[4]	4,532	4,286
Long-term debt due within one year		8	261
Accounts payable		146	177
Accrued expenses		43	46
Other		15	11
Total current liabilities		528	780
Long-term debt		1,502	1,152
Other		52	48
Total liabilities	[4]	2,977	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		5	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		5	3
Property, plant and equipment, net		0	0
NDT funds		0	0
Unamortized energy contract assets		0	0
Other Assets, Noncurrent		9	10
Assets, Noncurrent		9	10
Assets		14	13
Long-term debt due within one year		6	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		6	21
Long-term debt		0	0
Asset retirement obligations, noncurrent		0	0
Other		0	0
Liabilities, Noncurrent		0	0
Total liabilities		$ 6	$ 21

[1] Exelon’s consolidated assets include $2,722 million and $10,200 million at September 30, 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 $1,088 million and $3,598 million at September 30, 2021 and December 31, 2020, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 17 — Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $2,704 million and $10,182 million at September 30, 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 $1,078 million and $3,572 million at September 30, 2021 and December 31, 2020, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 17 — Variable Interest Entities for additional information.

[3] PHI’s consolidated total assets include $18 million at both September 30, 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 $10 million and $26 million at September 30, 2021 and December 31, 2020, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 17 — Variable Interest Entities for additional information.

[4] ACE’s consolidated total assets include $14 million and $13 million at September 30, 2021 and December 31, 2020, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $6 million and $21 million at September 30, 2021 and December 31, 2020, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 17 — Variable Interest Entities for additional information.