Variable Interest Entities - Assets and Liabilities of Consolidated VIES (Details) - USD ($) $ in Millions		Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,578	$ 663	$ 2,129	$ 587
Restricted cash and cash equivalents		379	438	373	358
Accounts receivable, net
Customer		3,138	3,231
Unamortized energy contract assets		37	38
Inventory, net
Materials and supplies		1,443	1,425
Assets held for sale		11	958
Other current assets		1,780	1,609
Total current assets		12,348	12,562
Property, plant and equipment, net		82,120	82,584
NDT funds		15,400	14,464
Unamortized energy contract assets		278	294
Other Assets, Noncurrent		2,964	2,982
Total assets	[1]	129,396	129,317
Long-term debt due within one year		3,633	1,819
Accounts payable		3,547	3,562
Accrued expenses		1,719	2,078
Unamortized energy contract liabilities		95	100
Liabilities held for sale		2	375
Other		1,139	1,264
Total current liabilities		13,919	12,771
Long-term debt		35,077	35,093
Asset retirement obligations, noncurrent		12,502	12,300
Unamortized energy contract liabilities		192	238
Other		2,848	2,942
Total liabilities	[1]	94,896	94,449
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		233	98
Restricted cash and cash equivalents		57	47
Accounts receivable, net
Customer		169	148
Other		44	36
Unamortized energy contract assets		22	22
Inventory, net
Materials and supplies		255	244
Assets held for sale		0	101
Other current assets		408	674
Total current assets		1,188	1,370
Property, plant and equipment, net		5,656	5,803
NDT funds		3,215	3,007
Unamortized energy contract assets		237	249
Other Assets, Noncurrent		35	52
Total noncurrent assets		9,143	9,111
Total assets		10,331	10,481
Long-term debt due within one year		84	94
Accounts payable		67	81
Accrued expenses		56	70
Unamortized energy contract liabilities		1	4
Liabilities held for sale		0	16
Other		1	5
Total current liabilities		209	270
Long-term debt		860	889
Asset retirement obligations, noncurrent		2,377	2,318
Other		133	129
Total noncurrent liabilities		3,370	3,336
Total liabilities		3,579	3,606
Unrestricted Assets [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Accounts receivable, net
Unamortized energy contract assets		22	22
Inventory, net
Assets held for sale		0	9
Unamortized energy contract assets		216	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		542	226	483	303
Restricted cash and cash equivalents		59	89	153	146
Accounts receivable, net
Customer		1,335	1,298
Unamortized energy contract assets		37	38
Inventory, net
Materials and supplies		986	978
Assets held for sale		11	958
Other current assets		1,353	1,357
Total current assets		6,209	6,947
Property, plant and equipment, net		19,837	22,214
NDT funds		15,400	14,464
Unamortized energy contract assets		278	293
Other Assets, Noncurrent		1,725	1,826
Total assets	[2]	45,821	48,094
Long-term debt due within one year		1,229	197
Accounts payable		1,489	1,253
Accrued expenses		654	788
Unamortized energy contract liabilities		4	7
Liabilities held for sale		2	375
Other		313	444
Total current liabilities		5,513	5,219
Long-term debt		4,627	5,566
Asset retirement obligations, noncurrent		12,257	12,054
Unamortized energy contract liabilities		3	3
Other		1,266	1,308
Total liabilities	[2]	32,836	33,418
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		233	98
Restricted cash and cash equivalents		54	44
Accounts receivable, net
Customer		169	148
Other		44	36
Unamortized energy contract assets		22	22
Inventory, net
Materials and supplies		255	244
Assets held for sale		0	101
Other current assets		404	669
Total current assets		1,181	1,362
Property, plant and equipment, net		5,656	5,803
NDT funds		3,215	3,007
Unamortized energy contract assets		237	249
Other Assets, Noncurrent		26	42
Total noncurrent assets		9,134	9,101
Total assets		10,315	10,463
Long-term debt due within one year		69	68
Accounts payable		67	81
Accrued expenses		56	70
Unamortized energy contract liabilities		1	4
Liabilities held for sale		0	16
Other		1	5
Total current liabilities		194	244
Long-term debt		860	889
Asset retirement obligations, noncurrent		2,377	2,318
Other		133	129
Total noncurrent liabilities		3,370	3,336
Total liabilities		3,564	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		22	22
Inventory, net
Assets held for sale		0	9
Unamortized energy contract assets		216	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		61	111	39	131
Restricted cash and cash equivalents		42	39	36	36
Accounts receivable, net
Customer		524	525
Inventory, net
Materials and supplies		196	198
Other current assets		77	45
Total current assets		1,585	1,599
Property, plant and equipment, net		15,927	15,377
Other Assets, Noncurrent		295	307
Total assets	[3]	24,235	23,736
Long-term debt due within one year		300	347
Accounts payable		517	539
Accrued expenses		246	299
Unamortized energy contract liabilities		92	92
Other		131	141
Total current liabilities		1,914	2,154
Long-term debt		7,069	6,659
Asset retirement obligations, noncurrent		59	59
Unamortized energy contract liabilities		190	235
Other		590	622
Total liabilities	[3]	13,776	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		3	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		7	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		16	18
Long-term debt due within one year		15	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		15	26
Long-term debt		0	0
Asset retirement obligations, noncurrent		0	0
Other		0	0
Total noncurrent liabilities		0	0
Total liabilities		15	26
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		11	17	8	12
Restricted cash and cash equivalents		3	3	$ 3	$ 2
Accounts receivable, net
Customer		152	124
Inventory, net
Other current assets		5	3
Total current assets		353	326
Property, plant and equipment, net		3,614	3,475
Other Assets, Noncurrent		49	50
Total assets	[4]	4,473	4,286
Long-term debt due within one year		13	261
Accounts payable		170	177
Accrued expenses		38	46
Other		11	11
Total current liabilities		499	780
Long-term debt		1,502	1,152
Other		47	48
Total liabilities	[4]	2,957	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		3	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		3	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		12
Long-term debt due within one year		11	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		11	21
Long-term debt		0	0
Asset retirement obligations, noncurrent		0	0
Other		0	0
Total noncurrent liabilities		0	0
Total liabilities		$ 11	$ 21

[1] Exelon’s consolidated assets include $10,093 million and $10,200 million at June 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 $3,578 million and $3,598 million at June 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 $10,077 million and $10,182 million at June 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 $3,563 million and $3,572 million at June 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 $16 million and $18 million at June 30, 2021 and December 31, 2020, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $15 million and $26 million at June 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 $12 million and $13 million at June 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 $11 million and $21 million at June 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.