Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 880	$ 1,349	$ 787	$ 898
Restricted cash and cash equivalents		223	247	209	207
Accounts receivable, net
Customer		4,564	4,607
Other		1,062	1,256
Inventory, net
Materials and Supplies		1,380	1,351
Other current assets		1,406	1,238
Total current assets		12,476	13,360
Property, plant and equipment, net		77,460	76,707
NDT funds		12,302	11,661
Other Assets, Noncurrent		3,017	1,575
Total assets	[1]	121,593	119,666
Long-term debt due within one year		2,508	1,349
Accounts payable		3,327	3,800
Accrued expenses		1,725	2,112
Unamortized energy contract liabilities		151	149
Other Liabilities, Current		1,245	1,035
Total current liabilities		12,229	11,404
Long-term debt		32,960	34,075
Asset retirement obligations		9,967	9,679
Unamortized energy contract liabilities		432	463
Other Liabilities, Noncurrent		3,158	2,130
Total liabilities	[1]	87,889	86,596
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		125	414
Restricted cash and cash equivalents		58	66
Accounts receivable, net
Customer		152	146
Other		23	23
Inventory, net
Materials and Supplies		213	212
Other current assets		51	52
Total current assets	[2]	622	913
Property, plant and equipment, net		6,147	6,145
NDT funds		2,520	2,351
Other Assets, Noncurrent		257	258
Total noncurrent assets	[2]	8,924	8,754
Total assets	[2]	9,546	9,667
Long-term debt due within one year		567	87
Accounts payable		120	96
Accrued expenses		42	72
Unamortized energy contract liabilities		13	15
Other Liabilities, Current		6	3
Total current liabilities	[2]	748	273
Long-term debt		565	1,072
Asset retirement obligations		2,190	2,160
Unamortized energy contract liabilities		0	1
Other Liabilities, Noncurrent		69	42
Total noncurrent liabilities	[2]	2,824	3,275
Total liabilities	[2]	3,572	3,548
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		537	750	610	416
Restricted cash and cash equivalents		139	153	127	138
Accounts receivable, net
Customer		2,800	2,941
Other		367	562
Inventory, net
Materials and Supplies		965	963
Other current assets		1,013	883
Total current assets		7,721	8,433
Property, plant and equipment, net		24,034	23,981
NDT funds		12,302	11,661
Other Assets, Noncurrent		1,813	755
Total assets	[3]	48,682	47,556
Long-term debt due within one year		2,365	906
Accounts payable		1,566	1,847
Accrued expenses		675	898
Unamortized energy contract liabilities		28	31
Other Liabilities, Current		425	279
Total current liabilities		6,660	5,769
Long-term debt		5,487	6,989
Asset retirement obligations		9,737	9,450
Unamortized energy contract liabilities		16	20
Other Liabilities, Noncurrent		1,528	610
Total liabilities	[3]	32,986	32,048
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		125	414
Restricted cash and cash equivalents		55	62
Accounts receivable, net
Customer		152	146
Other		23	23
Inventory, net
Materials and Supplies		213	212
Other current assets		48	49
Total current assets		616	906
Property, plant and equipment, net		6,147	6,145
NDT funds		2,520	2,351
Other Assets, Noncurrent		232	232
Total noncurrent assets		8,899	8,728
Total assets		9,515	9,634
Long-term debt due within one year		545	66
Accounts payable		120	96
Accrued expenses		41	72
Unamortized energy contract liabilities		13	15
Other Liabilities, Current		6	3
Total current liabilities		725	252
Long-term debt		524	1,025
Asset retirement obligations		2,190	2,160
Unamortized energy contract liabilities		0	1
Other Liabilities, Noncurrent		69	42
Total noncurrent liabilities		2,783	3,228
Total liabilities		3,508	3,480
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		33	124	43	30
Restricted cash and cash equivalents		39	43	40	42
Accounts receivable, net
Customer		445	453
Other		189	177
Inventory, net
Materials and Supplies		184	163
Other current assets		54	75
Total current assets		1,453	1,533
Property, plant and equipment, net		13,619	13,446
Other Assets, Noncurrent		370	60
Total assets	[4]	22,294	21,984
Long-term debt due within one year		125	125
Accounts payable		441	496
Accrued expenses		253	256
Unamortized energy contract liabilities		123	119
Other Liabilities, Current		127	123
Total current liabilities		1,675	1,592
Long-term debt		6,119	6,134
Asset retirement obligations		52	52
Unamortized energy contract liabilities		416	442
Other Liabilities, Noncurrent		630	369
Total liabilities	[4]	13,004	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
Inventory, net
Materials and Supplies		0	0
Other current assets		3	3
Total current assets	[2]	6	7
Property, plant and equipment, net		0	0
NDT funds		0	0
Other Assets, Noncurrent		25	26
Total noncurrent assets	[2]	25	26
Total assets	[2]	31	33
Long-term debt due within one year		22	21
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities	[2]	23	22
Long-term debt		41	47
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities	[2]	41	47
Total liabilities	[2]	64	69
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		6	7	10	2
Restricted cash and cash equivalents		3	4	$ 7	$ 6
Accounts receivable, net
Customer		85	95
Other		52	55
Inventory, net
Other current assets		6	5
Total current assets		238	240
Property, plant and equipment, net		3,041	2,966
Other Assets, Noncurrent		64	40
Total assets	[5]	3,783	3,699
Long-term debt due within one year		19	18
Accounts payable		139	154
Accrued expenses		38	35
Other Liabilities, Current		10	4
Total current liabilities		492	422
Long-term debt		1,165	1,170
Other Liabilities, Noncurrent		46	27
Total liabilities	[5]	2,654	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
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
Other Assets, Noncurrent		19	19
Total noncurrent assets		19	19
Total assets		22	23
Long-term debt due within one year		19	18
Accounts payable		0	0
Accrued expenses		0	1
Unamortized energy contract liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities		19	19
Long-term debt		35	40
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other Liabilities, Noncurrent		0	0
Total noncurrent liabilities		35	40
Total liabilities		$ 54	$ 59

[1] Exelon’s consolidated assets include $9,546 million and $9,667 million at March 31, 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 $3,572 million and $3,548 million at March 31, 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] Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

[3] Generation’s consolidated assets include $9,515 million and $9,634 million at March 31, 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 $3,508 million and $3,480 million at March 31, 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.

[4] PHI’s consolidated total assets include $31 million and $33 million at March 31, 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 $64 million and $69 million at March 31, 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.

[5] ACE’s consolidated total assets include $22 million and $23 million at March 31, 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 $54 million and $59 million at March 31, 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.