Variable Interest Entities - Assets and Liabilities of Consolidated VIES (Details) - USD ($) $ in Millions		Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 2,129	$ 587	$ 735	$ 1,349
Restricted cash and cash equivalents		373	358	252	247
Accounts receivable, net
Customer		2,814	4,592
Unamortized energy contract asset		43	47
Inventory, net
Materials and supplies		1,508	1,456
Other current assets		2,139	1,253
Total current assets		12,533	12,037
Property, plant and equipment, net		81,748	80,233
NDT funds		12,730	13,190
Unamortized energy contract asset		321	336
Other Assets, Noncurrent		3,101	3,197
Total assets	[1]	126,313	124,977
Long-term debt due within one year		2,514	4,710
Accounts payable		3,047	3,560
Accrued expenses		1,616	1,981
Unamortized energy contract liabilities		113	132
Other Liabilities, Current		1,474	1,331
Total current liabilities		11,065	14,185
Long-term debt		36,112	31,329
Asset retirement obligations, noncurrent		11,059	10,846
Unamortized energy contract liabilities		292	338
Other Liabilities, Noncurrent		2,964	3,064
Total liabilities	[1]	91,442	90,404
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		483	303	575	750
Restricted cash and cash equivalents		153	146	122	153
Accounts receivable, net
Customer		1,084	2,893
Unamortized energy contract asset		44	47
Inventory, net
Materials and supplies		1,075	1,026
Other current assets		1,343	605
Total current assets		5,849	7,076
Property, plant and equipment, net		23,954	24,193
NDT funds		12,730	13,190
Unamortized energy contract asset		320	336
Other Assets, Noncurrent		1,821	1,960
Total assets	[2]	47,003	48,995
Long-term debt due within one year		785	2,624
Accounts payable		1,075	1,692
Accrued expenses		621	786
Unamortized energy contract liabilities		9	17
Other Liabilities, Current		430	517
Total current liabilities		4,838	7,289
Long-term debt		5,768	4,464
Asset retirement obligations, noncurrent		10,819	10,603
Unamortized energy contract liabilities		10	11
Other Liabilities, Noncurrent		1,335	1,415
Total liabilities	[2]	31,776	33,165
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		39	131	54	124
Restricted cash and cash equivalents		36	36	37	43
Accounts receivable, net
Customer		492	479
Inventory, net
Materials and supplies		187	190
Other current assets		75	49
Total current assets		1,492	1,480
Property, plant and equipment, net		14,692	14,296
Other Assets, Noncurrent		309	323
Total assets	[3]	23,004	22,719
Long-term debt due within one year		350	103
Accounts payable		486	462
Accrued expenses		238	296
Unamortized energy contract liabilities		103	115
Other Liabilities, Current		128	131
Total current liabilities		1,685	1,612
Long-term debt		6,540	6,460
Asset retirement obligations, noncurrent		57	57
Unamortized energy contract liabilities		282	327
Other Liabilities, Noncurrent		549	577
Total liabilities	[3]	13,103	13,111
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		8	12	4	7
Restricted cash and cash equivalents		3	2	$ 2	$ 4
Accounts receivable, net
Customer		117	108
Inventory, net
Other current assets		4	5
Total current assets		321	270
Property, plant and equipment, net		3,302	3,190
Other Assets, Noncurrent		50	53
Total assets	[4]	4,089	3,933
Long-term debt due within one year		260	20
Accounts payable		170	144
Accrued expenses		39	42
Other Liabilities, Current		8	9
Total current liabilities		582	360
Long-term debt		1,160	1,307
Other Liabilities, Noncurrent		40	39
Total liabilities	[4]	2,701	2,657
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		114	163
Restricted cash and cash equivalents		105	88
Accounts receivable, net
Customer		145	151
Other		38	39
Unamortized energy contract asset		22	23
Inventory, net
Materials and supplies		236	227
Other current assets		675	32
Total current assets		1,335	723
Property, plant and equipment, net		5,939	6,022
NDT funds		2,642	2,741
Unamortized energy contract asset		258	250
Other Assets, Noncurrent		44	89
Total noncurrent assets		8,883	9,102
Total assets		10,218	9,825
Long-term debt due within one year		191	544
Accounts payable		71	106
Accrued expenses		60	70
Unamortized energy contract liabilities		6	8
Other Liabilities, Current		6	3
Total current liabilities		334	731
Long-term debt		947	527
Asset retirement obligations, noncurrent		2,182	2,128
Unamortized energy contract liabilities		1	1
Other Liabilities, Noncurrent		80	89
Total noncurrent liabilities		3,210	2,745
Total liabilities		3,544	3,476
PP&E - unrestricted asset		1	20
Variable Interest Entity, Primary Beneficiary [Member] | Recourse [Member]
Inventory, net
Total liabilities		2	3
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		114	163
Restricted cash and cash equivalents		102	85
Accounts receivable, net
Customer		145	151
Other		38	39
Unamortized energy contract asset		22	23
Inventory, net
Materials and supplies		236	227
Other current assets		671	31
Total current assets		1,328	719
Property, plant and equipment, net		5,939	6,022
NDT funds		2,642	2,741
Unamortized energy contract asset		258	250
Other Assets, Noncurrent		30	73
Total noncurrent assets		8,869	9,086
Total assets		10,197	9,805
Long-term debt due within one year		167	523
Accounts payable		71	106
Accrued expenses		60	70
Unamortized energy contract liabilities		6	8
Other Liabilities, Current		6	3
Total current liabilities		310	710
Long-term debt		934	504
Asset retirement obligations, noncurrent		2,182	2,128
Unamortized energy contract liabilities		1	1
Other Liabilities, Noncurrent		80	89
Total noncurrent liabilities		3,197	2,722
Total liabilities		3,507	3,432
PP&E - unrestricted asset		1	20
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member] | Recourse [Member]
Inventory, net
Total liabilities		2	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		3	3
Accounts receivable, net
Customer		0	0
Other		0	0
Unamortized energy contract asset		0	0
Inventory, net
Materials and supplies		0	0
Other current assets		4	1
Total current assets		7	4
Property, plant and equipment, net		0	0
NDT funds		0	0
Unamortized energy contract asset		0	0
Other Assets, Noncurrent		14	16
Total noncurrent assets		14	16
Total assets		21	20
Long-term debt due within one year		24	21
Accounts payable		0	0
Accrued expenses		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities		24	21
Long-term debt		13	23
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		13	23
Total liabilities		37	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		3	3
Accounts receivable, net
Customer		0	0
Other		0	0
Unamortized energy contract asset		0	0
Inventory, net
Materials and supplies		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 asset		0	0
Other Assets, Noncurrent		11	14
Total noncurrent assets		11	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 Liabilities, Current		0	0
Total current liabilities		20	20
Long-term debt		11	21
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		11	21
Total liabilities		31	41
Carrying amount of equity method investments | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		0	0
Carrying amount of equity method investments | Equity Investment VIE [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		$ 0	$ 0

[1] Exelon’s consolidated assets include $9,937 million and $9,532 million at June 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 $3,542 million and $3,473 million at June 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 $9,916 million and $9,512 million at June 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 $3,505 million and $3,429 million at June 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 $21 million and $20 million at June 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 $37 million and $44 million at June 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 June 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 $31 million and $41 million at June 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.