Variable Interest Entities - Assets and Liabilities of Consolidated VIES (Details) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,858	$ 587	$ 1,683	$ 1,349
Restricted cash and cash equivalents		485	358	309	247
Accounts receivable, net
Customer		2,792	4,592
Unamortized energy contract assets		41	47
Inventory, net
Materials and supplies		1,405	1,456
Other current assets		2,277	1,253
Total current assets		12,312	12,037
Property, plant and equipment, net		82,561	80,233
NDT funds		13,432	13,190
Unamortized energy contract assets		308	336
Other Assets, Noncurrent		3,165	3,197
Total assets	[1]	127,767	124,977
Long-term debt due within one year		2,077	4,710
Accounts payable		3,182	3,560
Accrued expenses		1,879	1,981
Unamortized energy contract liabilities		107	132
Other		1,475	1,331
Total current liabilities		11,262	14,185
Long-term debt		35,512	31,329
Asset retirement obligations, noncurrent		11,989	10,846
Unamortized energy contract liabilities		266	338
Other		3,313	3,064
Total liabilities	[1]	92,664	90,404
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		623	303	1,019	750
Restricted cash and cash equivalents		100	146	126	153
Accounts receivable, net
Customer		1,056	2,893
Unamortized energy contract assets		41	47
Inventory, net
Materials and supplies		971	1,026
Other current assets		1,387	605
Total current assets		5,883	7,076
Property, plant and equipment, net		23,709	24,193
NDT funds		13,432	13,190
Unamortized energy contract assets		308	336
Other Assets, Noncurrent		1,820	1,960
Total assets	[2]	47,372	48,995
Long-term debt due within one year		203	2,624
Accounts payable		1,109	1,692
Accrued expenses		699	786
Unamortized energy contract liabilities		8	17
Other		437	517
Total current liabilities		4,411	7,289
Long-term debt		5,677	4,464
Asset retirement obligations, noncurrent		11,744	10,603
Unamortized energy contract liabilities		8	11
Other		1,488	1,415
Total liabilities	[2]	32,448	33,165
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		196	131	99	124
Restricted cash and cash equivalents		38	36	38	43
Accounts receivable, net
Customer		495	479
Inventory, net
Materials and supplies		194	190
Other current assets		52	49
Total current assets		1,634	1,480
Property, plant and equipment, net		14,954	14,296
Other Assets, Noncurrent		300	323
Total assets	[3]	23,394	22,719
Long-term debt due within one year		349	103
Accounts payable		507	462
Accrued expenses		279	296
Unamortized energy contract liabilities		98	115
Other		144	131
Total current liabilities		1,723	1,612
Long-term debt		6,671	6,460
Asset retirement obligations, noncurrent		58	57
Unamortized energy contract liabilities		258	327
Other		650	577
Total liabilities	[3]	13,325	13,111
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		13	12	13	7
Restricted cash and cash equivalents		4	2	$ 3	$ 4
Accounts receivable, net
Customer		133	108
Inventory, net
Other current assets		4	5
Total current assets		340	270
Property, plant and equipment, net		3,372	3,190
Other Assets, Noncurrent		50	53
Total assets	[4]	4,201	3,933
Long-term debt due within one year		261	20
Accounts payable		168	144
Accrued expenses		42	42
Other		10	9
Total current liabilities		693	360
Long-term debt		1,156	1,307
Other		52	39
Total liabilities	[4]	2,813	2,657
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		148	163
Restricted cash and cash equivalents		52	88
Accounts receivable, net
Customer		151	151
Other		39	39
Unamortized energy contract assets		22	23
Inventory, net
Materials and supplies		241	227
Other current assets		781	32
Total current assets		1,434	723
Property, plant and equipment, net		5,865	6,022
NDT funds		2,785	2,741
Unamortized energy contract assets		253	250
Other Assets, Noncurrent		49	89
Total noncurrent assets		8,952	9,102
Total assets		10,386	9,825
Long-term debt due within one year		134	544
Accounts payable		81	106
Accrued expenses		63	70
Unamortized energy contract liabilities		5	8
Other		26	3
Total current liabilities		309	731
Long-term debt		913	527
Asset retirement obligations, noncurrent		2,210	2,128
Unamortized energy contract liabilities		1	1
Other		106	89
Total noncurrent liabilities		3,230	2,745
Total liabilities		3,539	3,476
PP&E - unrestricted asset		1	20
Other Assets		8	0
Variable Interest Entity, Primary Beneficiary [Member] | Recourse [Member]
Inventory, net
Total liabilities		8	3
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		148	163
Restricted cash and cash equivalents		48	85
Accounts receivable, net
Customer		151	151
Other		39	39
Unamortized energy contract assets		22	23
Inventory, net
Materials and supplies		241	227
Other current assets		776	31
Total current assets		1,425	719
Property, plant and equipment, net		5,865	6,022
NDT funds		2,785	2,741
Unamortized energy contract assets		253	250
Other Assets, Noncurrent		38	73
Total noncurrent assets		8,941	9,086
Total assets		10,366	9,805
Long-term debt due within one year		109	523
Accounts payable		81	106
Accrued expenses		63	70
Unamortized energy contract liabilities		5	8
Other		26	3
Total current liabilities		284	710
Long-term debt		906	504
Asset retirement obligations, noncurrent		2,210	2,128
Unamortized energy contract liabilities		1	1
Other		106	89
Total noncurrent liabilities		3,223	2,722
Total liabilities		3,507	3,432
PP&E - unrestricted asset		1	20
Other Assets		8	0
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member] | Recourse [Member]
Inventory, net
Total liabilities		8	3
Variable Interest Entity, Primary Beneficiary [Member] | Pepco Holdings LLC [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
Other current assets		5	1
Total current assets		9	4
Property, plant and equipment, net		0	0
NDT funds		0	0
Unamortized energy contract assets		0	0
Other Assets, Noncurrent		11	16
Total noncurrent assets		11	16
Total assets		20	20
Long-term debt due within one year		25	21
Accounts payable		0	0
Accrued expenses		0	0
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		25	21
Long-term debt		7	23
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other		0	0
Total noncurrent liabilities		7	23
Total liabilities		32	44
Variable Interest Entity, Primary Beneficiary [Member] | Atlantic City Electric Company [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
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		10	14
Total noncurrent assets		10	14
Total assets		14	17
Long-term debt due within one year		20	20
Accounts payable		0	0
Accrued expenses		0	0
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		20	20
Long-term debt		6	21
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other		0	0
Total noncurrent liabilities		6	21
Total liabilities		$ 26	$ 41

[1] Exelon’s consolidated assets include $10,102 million and $9,532 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,531 million and $3,473 million at September 30, 2020 and December 31, 2019, 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 $10,082 million and $9,512 million at September 30, 2020 and December 31, 2019, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,499 million and $3,429 million at September 30, 2020 and December 31, 2019, 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 $20 million and $20 million at September 30, 2020 and December 31, 2019, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $32 million and $44 million at September 30, 2020 and December 31, 2019, 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 $14 million and $17 million at September 30, 2020 and December 31, 2019, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $26 million and $41 million at September 30, 2020 and December 31, 2019, 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.