Variable Interest Entities Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016		Mar. 23, 2016	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 898		$ 635			$ 6,502	$ 1,878
Restricted cash		207		253
Customer		4,401		4,158
Other		1,132		1,201
Mark-to-market derivative assets		976		917
Materials and supplies		1,311		1,274
Other current assets		1,242		930
Total current assets		11,834		12,412
Property, plant and equipment, net		74,202		71,555
Nuclear decommissioning trust funds		13,272		11,061
Goodwill		6,677		6,677			2,672
Mark-to-market derivative assets		337		492
Other noncurrent assets		1,322		1,472
Total assets (a)	[1]	116,700		114,904
Long-term debt due within one year		2,088		2,430
Accounts payable		3,532		3,441
Accrued expenses		1,835		3,460
Mark-to-market derivative liabilities		232		282
Unamortized energy contract liabilities		231		407
Other current liabilities		982		981
Total current liabilities		10,796		13,457
Long-term debt		32,176		31,575
Asset retirement obligations		10,029		9,111
Pension obligations		3,736		4,248
Unamortized energy contract liabilities		609		830
Other noncurrent liabilities		2,097		1,827
Total liabilities	[1]	84,568		87,292
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		126	[2]	150	[3],[4]
Restricted cash		64	[2]	59	[3],[4]
Customer		138	[2]	371	[3],[4]
Other		25	[2]	48	[3],[4]
Mark-to-market derivative assets	[3],[4]			31
Materials and supplies		205	[2]	199	[3],[4]
Other current assets		45	[2]	50	[3],[4]
Total current assets		603	[2]	908	[3],[4]
Property, plant and equipment, net		6,186	[2]	5,415	[3],[4]
Nuclear decommissioning trust funds		2,502	[2]	2,185	[3],[4]
Goodwill	[3],[4]			47
Mark-to-market derivative assets	[3],[4]			23
Other noncurrent assets		274	[2]	315	[3],[4]
Total noncurrent assets		8,962	[2]	7,985	[3],[4]
Total assets (a)		9,565	[2]	8,893	[3],[4]
Long-term debt due within one year		102	[2]	181	[3],[4]
Accounts payable		114	[2]	269	[3],[4]
Accrued expenses		65	[2]	119	[3],[4]
Mark-to-market derivative liabilities	[3],[4]			60
Unamortized energy contract liabilities		18	[2]	15	[3],[4]
Other current liabilities		7	[2]	30	[3],[4]
Total current liabilities		306	[2]	674	[3],[4]
Long-term debt		1,154	[2]	641	[3],[4]
Asset retirement obligations		2,035	[2]	1,904	[3],[4]
Pension obligations	[3],[4],[5]			9
Unamortized energy contract liabilities		5	[2]	22	[3],[4]
Other noncurrent liabilities		112	[2]	106	[3],[4]
Noncurrent liabilities		3,306	[2]	2,682	[3],[4]
Total liabilities		3,612	[2]	3,356	[3],[4]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		416		290			431	780
Restricted cash		138		158
Customer		2,653		2,433
Other		321		558
Mark-to-market derivative assets		976		917
Materials and supplies		937		935
Other current assets		915		701
Total current assets		6,820		6,528
Property, plant and equipment, net		24,906		25,585
Nuclear decommissioning trust funds		13,272		11,061
Goodwill		47		47			47
Mark-to-market derivative assets		334		476
Other noncurrent assets		662		688
Total assets (a)	[6]	48,387		46,974
Long-term debt due within one year		346		1,117
Accounts payable		1,773		1,610
Accrued expenses		1,020		989
Mark-to-market derivative liabilities		211		263
Unamortized energy contract liabilities		43		72
Other current liabilities		265		313
Total current liabilities		4,189		5,683
Long-term debt		7,734		7,202
Asset retirement obligations		9,844		8,922
Unamortized energy contract liabilities		48		80
Other noncurrent liabilities		658		595
Total liabilities	[6]	32,483		33,718
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		126		150
Restricted cash		58		27
Customer		138		371
Other		25		48
Mark-to-market derivative assets				31
Materials and supplies		205		199
Other current assets		41		44
Total current assets		593		870
Property, plant and equipment, net		6,186		5,415
Nuclear decommissioning trust funds		2,502		2,185
Goodwill				47
Mark-to-market derivative assets				23
Other noncurrent assets		243		277
Total noncurrent assets		8,931		7,947
Total assets (a)		9,524		8,817
Long-term debt due within one year		67		99
Accounts payable		114		269
Accrued expenses		64		116
Mark-to-market derivative liabilities				60
Unamortized energy contract liabilities		18		15
Other current liabilities		7		30
Total current liabilities		270		589
Long-term debt		1,088		540
Asset retirement obligations		2,035		1,904
Pension obligations	[5]			9
Unamortized energy contract liabilities		5		22
Other noncurrent liabilities		112		106
Noncurrent liabilities		3,240		2,581
Total liabilities		3,510		3,170
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		17		23			9	64
Restricted cash		1		24
Customer		375		395
Other		94		102
Materials and supplies		40		38
Other current assets		3		7
Total current assets		811		842
Property, plant and equipment, net		7,602		7,040
Other noncurrent assets		4		9
Total assets (a)	[7]	9,104		8,704
Long-term debt due within one year		0		41
Accounts payable		265		205
Accrued expenses		164		175
Other current liabilities		24		26
Total current liabilities		760		707
Long-term debt		2,577		2,281
Asset retirement obligations		23		21
Other noncurrent liabilities		56		61
Total liabilities	[7]	5,963		5,856
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents				0
Restricted cash				23
Customer				0
Other				0
Mark-to-market derivative assets				0
Materials and supplies				0
Other current assets				0
Total current assets				23
Property, plant and equipment, net				0
Nuclear decommissioning trust funds				0
Goodwill				0
Mark-to-market derivative assets				0
Other noncurrent assets				3
Total noncurrent assets				3
Total assets (a)				26
Long-term debt due within one year				41
Accounts payable				0
Accrued expenses				1
Mark-to-market derivative liabilities				0
Unamortized energy contract liabilities				0
Other current liabilities				0
Total current liabilities				42
Long-term debt				0
Asset retirement obligations				0
Pension obligations	[5]			0
Unamortized energy contract liabilities				0
Other noncurrent liabilities				0
Noncurrent liabilities				0
Total liabilities				42
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		30		170
Restricted cash		42		43
Customer		486		496
Other		206		283
Materials and supplies		151		116
Other current assets		75		71
Total current assets		1,551		1,838
Property, plant and equipment, net		12,498		11,598
Goodwill		4,005		4,005		$ 0
Other noncurrent assets		70		81
Total assets (a)	[8]	21,247		21,025
Long-term debt due within one year		396		253
Accounts payable		348		458
Accrued expenses		261		272
Unamortized energy contract liabilities		188		335
Other current liabilities		81		47
Total current liabilities		1,931		2,284
Long-term debt		5,478		5,645
Asset retirement obligations		16		14
Unamortized energy contract liabilities		561		750
Other noncurrent liabilities		389		249
Total liabilities	[8]	12,422		13,009
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	[2]	0	[3]
Restricted cash		6	[2]	9	[3]
Customer		0	[2]	0	[3]
Other		0	[2]	0	[3]
Mark-to-market derivative assets	[3]			0
Materials and supplies		0	[2]	0	[3]
Other current assets		4	[2]	5	[3]
Total current assets		10	[2]	14	[3]
Property, plant and equipment, net		0	[2]	0	[3]
Nuclear decommissioning trust funds		0	[2]	0	[3]
Goodwill	[3]			0
Mark-to-market derivative assets	[3]			0
Other noncurrent assets		31	[2]	35	[3]
Total noncurrent assets		31	[2]	35	[3]
Total assets (a)		41	[2]	49	[3]
Long-term debt due within one year		35	[2]	40	[3]
Accounts payable		0	[2]	0	[3]
Accrued expenses		1	[2]	2	[3]
Mark-to-market derivative liabilities	[3]			0
Unamortized energy contract liabilities		0	[2]	0	[3]
Other current liabilities		0	[2]	0	[3]
Total current liabilities		36	[2]	42	[3]
Long-term debt		66	[2]	101	[3]
Asset retirement obligations		0	[2]	0	[3]
Pension obligations	[3],[5]			0
Unamortized energy contract liabilities		0	[2]	0	[3]
Other noncurrent liabilities		0	[2]	0	[3]
Noncurrent liabilities		66	[2]	101	[3]
Total liabilities		102	[2]	143	[3]
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		2		101			$ 3	$ 2
Restricted cash		6		9
Customer		92		125
Other		56		44
Other current assets		2		2
Total current assets		258		399
Property, plant and equipment, net		2,706		2,521
Other noncurrent assets		45		44
Total assets (a)	[9]	3,445		3,457
Long-term debt due within one year		281		35
Accounts payable		118		132
Accrued expenses		33		38
Other current liabilities		8		8
Total current liabilities		619		320
Long-term debt		840		1,120
Other noncurrent liabilities		25		32
Total liabilities	[9]	2,402		2,423
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0		0
Restricted cash		6		9
Customer		0		0
Other		0		0
Mark-to-market derivative assets				0
Materials and supplies		0		0
Other current assets		0		0
Total current assets		6		9
Property, plant and equipment, net		0		0
Nuclear decommissioning trust funds		0		0
Goodwill				0
Mark-to-market derivative assets				0
Other noncurrent assets		23		23
Total noncurrent assets		23		23
Total assets (a)		29		32
Long-term debt due within one year		31		35
Accounts payable		0		0
Accrued expenses		1		2
Mark-to-market derivative liabilities				0
Unamortized energy contract liabilities		0		0
Other current liabilities		0		0
Total current liabilities		32		37
Long-term debt		58		89
Asset retirement obligations		0		0
Pension obligations	[5]			0
Unamortized energy contract liabilities		0		0
Other noncurrent liabilities		0		0
Noncurrent liabilities		58		89
Total liabilities		$ 90		$ 126

[1] Exelon’s consolidated assets include $9,565 million and $8,893 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,612 million and $3,356 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.

[2] Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity

[3] Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

[4] Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

[5] Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 16 - Retirement Benefits for additional details.

[6] Generation’s consolidated assets include $9,524 million and $8,817 million at December 31, 2017 and 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,510 million and $3,170 million at December 31, 2017 and 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.

[7] BGE’s consolidated assets include $26 million at December 31, 2016 of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $42 million at December 31, 2016 of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. BGE no longer has interests in any VIEs as of December 31, 2017. See Note 2 - Variable Interest Entities.

[8] PHI’s consolidated total assets include $41 million and $49 million at December 31, 2017 and 2016, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $102 million and $143 million at December 31, 2017 and 2016, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 - Variable Interest Entities.

[9] ACE’s consolidated assets include $29 million and $32 million at December 31, 2017 and 2016, respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $90 million and $126 million at December 31, 2017 and 2016, respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 - Variable Interest Entities.