Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) - USD ($) $ in Millions		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents		$ 587		$ 1,349		$ 898	$ 635
Restricted cash		358		247		207	253
Accounts Receivable, net
Customer		4,592		4,607
Other		1,583		1,256
Unamortized energy contract assets, current		47		48
Inventories, net
Materials and supplies		1,456		1,351
Other current assets		1,253		1,238
Total current assets		12,037		13,328
Property, plant and equipment, net		80,233		76,707
Nuclear decommissioning trust funds		13,190		11,661
Unamortized energy contract assets, noncurrent		336		372
Other Assets, Noncurrent		3,197		1,575
Total assets	[1]	124,977		119,634
Current liabilities
Long-term debt due within one year		4,710		1,349
Accounts payable		3,560		3,800
Accrued expenses		1,981		2,112
Unamortized energy contract liabilities		132		149
Other current liabilities		1,331		1,035
Total current liabilities		14,185		11,404
Long-term debt		31,329		34,075
Asset retirement obligations		10,846		9,679
Unamortized energy contract liabilities		338		463
Other Liabilities, Noncurrent		3,064		2,130
Total liabilities		90,404		86,587	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		163		414
Restricted cash		88		66
Accounts Receivable, net
Customer		151		146
Other		39		23
Unamortized energy contract assets, current		23		25
Inventories, net
Materials and supplies		227		212
Other current assets		32		52
Total current assets		723		938
Property, plant and equipment, net		6,022		6,188
Nuclear decommissioning trust funds		2,741		2,351
Unamortized energy contract assets, noncurrent		250		274
Other Assets, Noncurrent		89		258
Total noncurrent assets		9,102		9,071
Total assets		9,825		10,009
Current liabilities
Long-term debt due within one year		544		87
Accounts payable		106		96
Accrued expenses		70		73
Unamortized energy contract liabilities		8		15
Other current liabilities		3		3
Total current liabilities		731		274
Long-term debt		527		1,072
Asset retirement obligations		2,128		2,165
Unamortized energy contract liabilities		1		1
Other Liabilities, Noncurrent		89		42
Total noncurrent liabilities		2,745		3,280
Total liabilities		3,476		3,554
PP&E - unrestricted asset				43
Variable Interest Entity, Consolidated, Liabilities, Recourse		3		5
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		303		750		416	290
Restricted cash		146		153		138	158
Accounts Receivable, net
Customer		2,893		2,941
Other		619		562
Unamortized energy contract assets, current		47		49
Inventories, net
Materials and supplies		1,026		963
Other current assets		941		883
Total current assets		7,076		8,433
Property, plant and equipment, net		24,193		23,981
Nuclear decommissioning trust funds		13,190		11,661
Unamortized energy contract assets, noncurrent		336		371
Other Assets, Noncurrent		1,960		755
Total assets	[2]	48,995		47,556
Current liabilities
Long-term debt due within one year		2,624		906
Accounts payable		1,692		1,847
Accrued expenses		786		898
Unamortized energy contract liabilities		17		31
Other current liabilities		517		279
Total current liabilities		7,289		5,769
Long-term debt		4,464		6,989
Asset retirement obligations		10,603		9,450
Unamortized energy contract liabilities		11		20
Other Liabilities, Noncurrent		1,415		610
Total liabilities	[2]	33,165		32,048
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		163		414
Restricted cash		85		62
Accounts Receivable, net
Customer		151		146
Other		39		23
Unamortized energy contract assets, current		23		25
Inventories, net
Materials and supplies		227		212
Other current assets		31		49
Total current assets		719		931
Property, plant and equipment, net		6,022		6,188
Nuclear decommissioning trust funds		2,741		2,351
Unamortized energy contract assets, noncurrent		250		274
Other Assets, Noncurrent		73		232
Total noncurrent assets		9,086		9,045
Total assets		9,805		9,976
Current liabilities
Long-term debt due within one year		523		66
Accounts payable		106		96
Accrued expenses		70		72
Unamortized energy contract liabilities		8		15
Other current liabilities		3		3
Total current liabilities		710		252
Long-term debt		504		1,025
Asset retirement obligations		2,128		2,165
Unamortized energy contract liabilities		1		1
Other Liabilities, Noncurrent		89		42
Total noncurrent liabilities		2,722		3,233
Total liabilities		3,432		3,485
PP&E - unrestricted asset		20		43
Variable Interest Entity, Consolidated, Liabilities, Recourse		3		5
Pepco Holdings LLC [Member]
Current assets
Cash and cash equivalents		131		124		30	170
Restricted cash		36		43		42	43
Accounts Receivable, net
Customer		479		453
Other		174		177
Inventories, net
Materials and supplies		190		163
Other current assets		49		75
Total current assets		1,480		1,501
Property, plant and equipment, net		14,296		13,446
Other Assets, Noncurrent		323		60
Total assets		22,719		21,952
Current liabilities
Long-term debt due within one year		103		125
Accounts payable		462		496
Accrued expenses		296		256
Unamortized energy contract liabilities		115		119
Other current liabilities		131		123
Total current liabilities		1,612		1,592
Long-term debt		6,460		6,134
Asset retirement obligations		57		52
Unamortized energy contract liabilities		327		442
Other Liabilities, Noncurrent		577		369
Total liabilities		13,111	[3]	12,693
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		0		0
Restricted cash		3		4
Accounts Receivable, net
Customer		0		0
Other		0		0
Unamortized energy contract assets, current		0		0
Inventories, net
Materials and supplies		0		0
Other current assets		1		3
Total current assets		4		7
Property, plant and equipment, net		0		0
Nuclear decommissioning trust funds		0		0
Unamortized energy contract assets, noncurrent		0		0
Other Assets, Noncurrent		16		26
Total noncurrent assets		16		26
Total assets		20		33
Current liabilities
Long-term debt due within one year		21		21
Accounts payable		0		0
Accrued expenses		0		1
Unamortized energy contract liabilities		0		0
Other current liabilities		0		0
Total current liabilities		21		22
Long-term debt		23		47
Asset retirement obligations		0		0
Unamortized energy contract liabilities		0		0
Other Liabilities, Noncurrent		0		0
Total noncurrent liabilities		23		47
Total liabilities		44		69
Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		12		7		2	101
Restricted cash		2		4		$ 6	$ 9
Accounts Receivable, net
Customer		108		95
Other		48		55
Inventories, net
Other current assets		5		5
Total current assets		270		240
Property, plant and equipment, net		3,190		2,966
Other Assets, Noncurrent		53		40
Total assets	[4]	3,933		3,699
Current liabilities
Long-term debt due within one year		20		18
Accounts payable		144		154
Accrued expenses		42		35
Other current liabilities		9		4
Total current liabilities		360		422
Long-term debt		1,307		1,170
Other Liabilities, Noncurrent		39		27
Total liabilities		2,657		2,573
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		0		0
Restricted cash		3		4
Accounts Receivable, net
Customer		0		0
Other		0		0
Unamortized energy contract assets, current		0		0
Inventories, net
Materials and supplies		0		0
Other current assets		0		0
Total current assets		3		4
Property, plant and equipment, net		0		0
Nuclear decommissioning trust funds		0		0
Unamortized energy contract assets, noncurrent		0		0
Other Assets, Noncurrent		14		19
Total noncurrent assets		14		19
Total assets		17		23
Current liabilities
Long-term debt due within one year		20		18
Accounts payable		0		0
Accrued expenses		0		1
Unamortized energy contract liabilities		0		0
Other current liabilities		0		0
Total current liabilities		20		19
Long-term debt		21		40
Asset retirement obligations		0		0
Unamortized energy contract liabilities		0		0
Other Liabilities, Noncurrent		0		0
Total noncurrent liabilities		21		40
Total liabilities		$ 41		$ 59

[1] Exelon’s consolidated assets include $9,532 million and $9,667 million at December 31, 2019 and 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,473 million and $3,548 million at December 31, 2019 and 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 22–Variable Interest Entities for additional information.

[2] Generation’s consolidated assets include $9,512 million and $9,634 million at December 31, 2019 and 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,429 million and $3,480 million at December 31, 2019 and 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 22–Variable Interest Entities for additional information.

[3] PHI’s consolidated total assets include $20 million and $33 million at December 31, 2019 and 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 $44 million and $69 million at December 31, 2019 and 2018, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 22 - Variable Interest Entities for additional information.

[4] ACE’s consolidated assets include $17 million and $23 million at December 31, 2019 and 2018, respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $41 million and $59 million at December 31, 2019 and 2018, respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 22 - Variable Interest Entities for additional information.