Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,683	$ 1,349	$ 1,918	$ 898
Restricted cash and cash equivalents		309	247	240	207
Accounts receivable, net
Customer		4,188	4,607
Other		1,085	1,256
Unamortized energy contract asset		49	48
Inventory, net
Materials and supplies		1,458	1,351
Other current assets		1,296	1,238
Total current assets		12,206	13,360
Property, plant and equipment, net		78,593	76,707
NDT funds		12,706	11,661
Unamortized energy contract asset		353	372
Other Assets, Noncurrent		3,123	1,575
Total assets	[1]	122,738	119,666
Long-term debt due within one year		4,248	1,349
Accounts payable		3,348	3,800
Accrued expenses		1,877	2,112
Unamortized energy contract liabilities		138	149
Other Liabilities, Current		1,425	1,035
Total current liabilities		13,085	11,404
Long-term debt		32,056	34,075
Asset retirement obligations, noncurrent		10,089	9,679
Unamortized energy contract liabilities		368	463
Other Liabilities, Noncurrent		3,123	2,130
Total liabilities	[1]	88,386	86,596
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		168	414
Restricted cash and cash equivalents		76	66
Accounts receivable, net
Customer		163	146
Other		43	23
Unamortized energy contract asset		23	25
Inventory, net
Materials and supplies		222	212
Other current assets		50	52
Total current assets		745	938
Property, plant and equipment, net		6,079	6,188
NDT funds		2,636	2,351
Unamortized energy contract asset		258	274
Other Assets, Noncurrent		69	258
Total noncurrent assets		9,042	9,071
Total assets		9,787	10,009
Long-term debt due within one year		556	87
Accounts payable		148	96
Accrued expenses		58	73
Unamortized energy contract liabilities		10	15
Other Liabilities, Current		30	3
Total current liabilities		802	274
Long-term debt		532	1,072
Asset retirement obligations, noncurrent		2,103	2,165
Unamortized energy contract liabilities		1	1
Other Liabilities, Noncurrent		84	42
Total noncurrent liabilities		2,720	3,280
Total liabilities		3,522	3,554
PP&E - unrestricted asset		41	43
Variable Interest Entity, Consolidated, Liabilities, Recourse		5	5
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		1,019	750	1,187	416
Restricted cash and cash equivalents		126	153	152	138
Accounts receivable, net
Customer		2,587	2,941
Other		337	562
Unamortized energy contract asset		49	49
Inventory, net
Materials and supplies		1,010	963
Other current assets		1,002	883
Total current assets		7,159	8,433
Property, plant and equipment, net		23,591	23,981
NDT funds		12,706	11,661
Unamortized energy contract asset		352	371
Other Assets, Noncurrent		1,915	755
Total assets	[2]	47,984	47,556
Long-term debt due within one year		2,706	906
Accounts payable		1,583	1,847
Accrued expenses		762	898
Unamortized energy contract liabilities		21	31
Other Liabilities, Current		541	279
Total current liabilities		6,344	5,769
Long-term debt		5,018	6,989
Asset retirement obligations, noncurrent		9,855	9,450
Unamortized energy contract liabilities		11	20
Other Liabilities, Noncurrent		1,466	610
Total liabilities	[2]	32,391	32,048
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		168	414
Restricted cash and cash equivalents		73	62
Accounts receivable, net
Customer		163	146
Other		43	23
Unamortized energy contract asset		23	25
Inventory, net
Materials and supplies		222	212
Other current assets		48	49
Total current assets		740	931
Property, plant and equipment, net		6,079	6,188
NDT funds		2,636	2,351
Unamortized energy contract asset		258	274
Other Assets, Noncurrent		52	232
Total noncurrent assets		9,025	9,045
Total assets		9,765	9,976
Long-term debt due within one year		535	66
Accounts payable		148	96
Accrued expenses		57	72
Unamortized energy contract liabilities		10	15
Other Liabilities, Current		30	3
Total current liabilities		780	252
Long-term debt		504	1,025
Asset retirement obligations, noncurrent		2,103	2,165
Unamortized energy contract liabilities		1	1
Other Liabilities, Noncurrent		84	42
Total noncurrent liabilities		2,692	3,233
Total liabilities		3,472	3,485
PP&E - unrestricted asset		41	43
Variable Interest Entity, Consolidated, Liabilities, Recourse		5	5
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		99	124	153	30
Restricted cash and cash equivalents		38	43	42	42
Accounts receivable, net
Customer		512	453
Other		189	177
Inventory, net
Materials and supplies		203	163
Other current assets		50	75
Total current assets		1,578	1,533
Property, plant and equipment, net		13,968	13,446
Other Assets, Noncurrent		356	60
Total assets	[3]	22,576	21,984
Long-term debt due within one year		118	125
Accounts payable		416	496
Accrued expenses		279	256
Unamortized energy contract liabilities		117	119
Other Liabilities, Current		152	123
Total current liabilities		1,515	1,592
Long-term debt		6,376	6,134
Asset retirement obligations, noncurrent		57	52
Unamortized energy contract liabilities		357	442
Other Liabilities, Noncurrent		610	369
Total liabilities	[3]	13,028	12,702
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	4
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		2	3
Total current assets		5	7
Property, plant and equipment, net		0	0
NDT funds		0	0
Unamortized energy contract asset		0	0
Other Assets, Noncurrent		17	26
Total noncurrent assets		17	26
Total assets		22	33
Long-term debt due within one year		21	21
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities		22	22
Long-term debt		28	47
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		28	47
Total liabilities		50	69
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		13	7	11	2
Restricted cash and cash equivalents		3	4	$ 7	$ 6
Accounts receivable, net
Customer		142	95
Other		47	55
Inventory, net
Other current assets		7	5
Total current assets		307	240
Property, plant and equipment, net		3,124	2,966
Other Assets, Noncurrent		59	40
Total assets	[4]	3,916	3,699
Long-term debt due within one year		19	18
Accounts payable		139	154
Accrued expenses		40	35
Other Liabilities, Current		11	4
Total current liabilities		347	422
Long-term debt		1,305	1,170
Other Liabilities, Noncurrent		44	27
Total liabilities	[4]	2,648	2,573
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	4
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	4
Property, plant and equipment, net		0	0
NDT funds		0	0
Unamortized energy contract asset		0	0
Other Assets, Noncurrent		15	19
Total noncurrent assets		15	19
Total assets		18	23
Long-term debt due within one year		19	18
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities		20	19
Long-term debt		26	40
Asset retirement obligations, noncurrent		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		26	40
Total liabilities		$ 46	$ 59

[1] Exelon’s consolidated assets include $9,465 million and $9,667 million at September 30, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,517 million and $3,548 million at September 30, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2 — Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $9,443 million and $9,634 million at September 30, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,467 million and $3,480 million at September 30, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2 — Variable Interest Entities for additional information.

[3] PHI’s consolidated total assets include $22 million and $33 million at September 30, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $50 million and $69 million at September 30, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 — Variable Interest Entities for additional information.

[4] ACE’s consolidated total assets include $18 million and $23 million at September 30, 2019 and December 31, 2018, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $46 million and $59 million at September 30, 2019 and December 31, 2018, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 — Variable Interest Entities for additional information.