Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,457	$ 587	$ 880	$ 1,349
Restricted cash and cash equivalents		414	358	223	247
Accounts receivable, net
Customer		4,042	4,592
Unamortized energy contract asset		47	47
Inventory, net
Materials and supplies		1,463	1,456
Other current assets		1,629	1,253
Total current assets		12,476	12,037
Property, plant and equipment, net		81,017	80,233
NDT funds		11,611	13,190
Unamortized energy contract asset		329	336
Other Assets, Noncurrent		3,164	3,197
Total assets	[1]	124,677	124,977
Long-term debt due within one year		2,848	4,710
Accounts payable		2,883	3,560
Accrued expenses		1,535	1,981
Unamortized energy contract liabilities		121	132
Other Liabilities, Current		1,276	1,331
Total current liabilities		11,774	14,185
Long-term debt		34,808	31,329
Asset retirement obligations, noncurrent		10,951	10,846
Unamortized energy contract liabilities		317	338
Other Liabilities, Noncurrent		3,017	3,064
Total liabilities	[1]	90,061	90,404
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		51	163
Restricted cash and cash equivalents		84	88
Accounts receivable, net
Customer		131	151
Other		44	39
Unamortized energy contract asset		22	23
Inventory, net
Materials and supplies		231	227
Other current assets		42	32
Total current assets		605	723
Property, plant and equipment, net		6,017	6,022
NDT funds		2,405	2,741
Unamortized energy contract asset		264	250
Other Assets, Noncurrent		71	89
Total noncurrent assets		8,757	9,102
Total assets		9,362	9,825
Long-term debt due within one year		543	544
Accounts payable		121	106
Accrued expenses		46	70
Unamortized energy contract liabilities		7	8
Other Liabilities, Current		3	3
Total current liabilities		720	731
Long-term debt		502	527
Asset retirement obligations, noncurrent		2,156	2,128
Unamortized energy contract liabilities		1	1
Other Liabilities, Noncurrent		37	89
Total noncurrent liabilities		2,696	2,745
Total liabilities		3,416	3,476
PP&E - unrestricted asset		20	20
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		821	303	537	750
Restricted cash and cash equivalents		150	146	139	153
Accounts receivable, net
Customer		2,415	2,893
Unamortized energy contract asset		47	47
Inventory, net
Materials and supplies		1,038	1,026
Other current assets		1,243	941
Total current assets		7,324	7,076
Property, plant and equipment, net		24,169	24,193
NDT funds		11,611	13,190
Unamortized energy contract asset		328	336
Other Assets, Noncurrent		1,941	1,960
Total assets	[2]	47,882	48,995
Long-term debt due within one year		1,623	2,624
Accounts payable		1,195	1,692
Accrued expenses		603	786
Unamortized energy contract liabilities		12	17
Other Liabilities, Current		434	517
Total current liabilities		6,325	7,289
Long-term debt		5,943	4,464
Asset retirement obligations, noncurrent		10,709	10,603
Unamortized energy contract liabilities		10	11
Other Liabilities, Noncurrent		1,424	1,415
Total liabilities	[2]	32,699	33,165
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		51	163
Restricted cash and cash equivalents		81	85
Accounts receivable, net
Customer		131	151
Other		44	39
Unamortized energy contract asset		22	23
Inventory, net
Materials and supplies		231	227
Other current assets		38	31
Total current assets		598	719
Property, plant and equipment, net		6,017	6,022
NDT funds		2,405	2,741
Unamortized energy contract asset		264	250
Other Assets, Noncurrent		56	73
Total noncurrent assets		8,742	9,086
Total assets		9,340	9,805
Long-term debt due within one year		519	523
Accounts payable		121	106
Accrued expenses		46	70
Unamortized energy contract liabilities		7	8
Other Liabilities, Current		3	3
Total current liabilities		696	710
Long-term debt		483	504
Asset retirement obligations, noncurrent		2,156	2,128
Unamortized energy contract liabilities		1	1
Other Liabilities, Noncurrent		37	89
Total noncurrent liabilities		2,677	2,722
Total liabilities		3,373	3,432
PP&E - unrestricted asset		20	20
Variable Interest Entity, Consolidated, Liabilities, Recourse		4	3
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		49	131	33	124
Restricted cash and cash equivalents		37	36	39	43
Accounts receivable, net
Customer		429	479
Inventory, net
Materials and supplies		187	190
Other current assets		57	49
Total current assets		1,369	1,480
Property, plant and equipment, net		14,491	14,296
Other Assets, Noncurrent		316	323
Total assets	[3]	22,753	22,719
Long-term debt due within one year		144	103
Accounts payable		423	462
Accrued expenses		280	296
Unamortized energy contract liabilities		109	115
Other Liabilities, Current		129	131
Total current liabilities		1,481	1,612
Long-term debt		6,564	6,460
Asset retirement obligations, noncurrent		57	57
Unamortized energy contract liabilities		307	327
Other Liabilities, Noncurrent		552	577
Total liabilities	[3]	13,027	13,111
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 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		15	16
Total noncurrent assets		15	16
Total assets		22	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		19	23
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		19	23
Total liabilities		43	44
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		8	12	6	7
Restricted cash and cash equivalents		3	2	$ 3	$ 4
Accounts receivable, net
Customer		92	108
Inventory, net
Other current assets		3	5
Total current assets		261	270
Property, plant and equipment, net		3,249	3,190
Other Assets, Noncurrent		51	53
Total assets	[4]	3,978	3,933
Long-term debt due within one year		60	20
Accounts payable		145	144
Accrued expenses		40	42
Other Liabilities, Current		8	9
Total current liabilities		460	360
Long-term debt		1,265	1,307
Other Liabilities, Noncurrent		37	39
Total liabilities	[4]	2,711	2,657
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 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		12	14
Total noncurrent assets		12	14
Total assets		15	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		16	21
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		16	21
Total liabilities		$ 36	$ 41

[1] Exelon’s consolidated assets include $9,056 million and $9,532 million at March 31, 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 $3,412 million and $3,473 million at March 31, 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 $9,034 million and $9,512 million at March 31, 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 $3,369 million and $3,429 million at March 31, 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 $22 million and $20 million at March 31, 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 $43 million and $44 million at March 31, 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 $15 million and $17 million at March 31, 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 $36 million and $41 million at March 31, 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.