Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 787	$ 898	$ 609	$ 635
Restricted cash		209	207	254	253
Accounts receivable, net
Customer		4,190	4,445
Other		1,103	1,132
Mark-to-market derivatives assets		978	976
Inventory
Materials and supplies		1,291	1,311
Other current assets		1,495	1,260
Total current assets		11,533	11,896
Property, plant and equipment, net		74,711	74,202
Nuclear decommissioning trust funds		13,149	13,272
Goodwill		6,677	6,677
Mark-to-market derivative assets		527	337
Other noncurrent assets		1,333	1,330
Total assets	[1]	117,018	116,770
Long-term debt due within one year		1,203	2,088
Accounts payable		3,207	3,532
Accrued expenses		1,569	1,837
Mark-to-market derivative liabilities		415	232
Unamortized energy contract liabilities		202	231
Other		956	982
Total current liabilities		10,153	10,798
Long-term debt		32,905	32,176
Asset retirement obligations		10,126	10,029
Pension obligation		3,433	3,736
Unamortized energy contract liabilities		579	609
Other noncurrent liabilities		2,067	2,097
Total liabilities	[1]	84,453	84,583
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	280	126
Restricted cash	[2]	73	64
Accounts receivable, net
Customer	[2]	154	170
Other	[2]	29	25
Inventory
Materials and supplies	[2]	202	205
Other current assets	[2]	55	45
Total current assets	[2]	793	635
Property, plant and equipment, net	[2]	6,181	6,186
Nuclear decommissioning trust funds	[2]	2,483	2,502
Other noncurrent assets	[2]	270	274
Total noncurrent assets	[2]	8,934	8,962
Total assets	[2]	9,727	9,597
Long-term debt due within one year	[2]	102	102
Accounts payable	[2]	93	114
Accrued expenses	[2]	52	67
Unamortized energy contract liabilities	[2]	17	18
Other	[2]	5	7
Total current liabilities	[2]	269	308
Long-term debt	[2]	1,125	1,154
Asset retirement obligations	[2]	2,062	2,035
Unamortized energy contract liabilities	[2]	1	5
Other noncurrent liabilities	[2]	99	116
Total noncurrent liabilities	[2]	3,287	3,310
Total liabilities	[2]	3,556	3,618
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		610	416	400	290
Restricted cash		127	138	140	158
Accounts receivable, net
Customer		2,478	2,697
Other		294	321
Mark-to-market derivatives assets		978	976
Inventory
Materials and supplies		916	937
Other current assets		1,122	933
Total current assets		6,884	6,882
Property, plant and equipment, net		24,714	24,906
Nuclear decommissioning trust funds		13,149	13,272
Goodwill		47	47
Mark-to-market derivative assets		527	334
Other noncurrent assets		657	670
Total assets	[3]	48,375	48,457
Long-term debt due within one year		373	346
Accounts payable		1,447	1,773
Accrued expenses		951	1,022
Mark-to-market derivative liabilities		391	211
Unamortized energy contract liabilities		39	43
Other		288	265
Total current liabilities		4,156	4,191
Long-term debt		7,685	7,734
Asset retirement obligations		9,941	9,844
Unamortized energy contract liabilities		40	48
Other noncurrent liabilities		686	658
Total liabilities	[3]	32,417	32,498
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		280	126
Restricted cash		66	58
Accounts receivable, net
Customer		154	170
Other		29	25
Inventory
Materials and supplies		202	205
Other current assets		51	41
Total current assets		782	625
Property, plant and equipment, net		6,181	6,186
Nuclear decommissioning trust funds		2,483	2,502
Other noncurrent assets		242	243
Total noncurrent assets		8,906	8,931
Total assets		9,688	9,556
Long-term debt due within one year		70	67
Accounts payable		93	114
Accrued expenses		51	66
Unamortized energy contract liabilities		17	18
Other		5	7
Total current liabilities		236	272
Long-term debt		1,063	1,088
Asset retirement obligations		2,062	2,035
Unamortized energy contract liabilities		1	5
Other noncurrent liabilities		99	116
Total noncurrent liabilities		3,225	3,244
Total liabilities		3,461	3,516
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		22	17	11	23
Restricted cash		2	1	43	24
Accounts receivable, net
Customer		394	375
Other		91	94
Inventory
Materials and supplies		45	40
Other current assets		5	3
Total current assets		755	811
Property, plant and equipment, net		7,725	7,602
Other noncurrent assets		6	4
Total assets		9,195	9,104
Accounts payable		253	265
Accrued expenses		162	164
Other		26	24
Total current liabilities		757	760
Long-term debt		2,578	2,577
Asset retirement obligations		22	23
Other noncurrent liabilities		53	56
Total liabilities		5,978	5,963
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		43	30	109	170
Restricted cash		40	42	41	43
Accounts receivable, net
Customer		484	486
Other		210	206
Inventory
Materials and supplies		152	151
Other current assets		55	75
Total current assets		1,493	1,551
Property, plant and equipment, net		12,688	12,498
Goodwill		4,005	4,005
Other noncurrent assets		69	70
Total assets	[4]	21,375	21,247
Long-term debt due within one year		385	396
Accounts payable		469	348
Accrued expenses		246	261
Unamortized energy contract liabilities		162	188
Other		52	81
Total current liabilities		2,067	1,931
Long-term debt		5,464	5,478
Asset retirement obligations		16	16
Unamortized energy contract liabilities		539	561
Other noncurrent liabilities		377	389
Total liabilities	[4]	12,556	12,422
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	0	0
Restricted cash	[2]	7	6
Accounts receivable, net
Customer	[2]	0	0
Other	[2]	0	0
Inventory
Materials and supplies	[2]	0	0
Other current assets	[2]	4	4
Total current assets	[2]	11	10
Property, plant and equipment, net	[2]	0	0
Nuclear decommissioning trust funds	[2]	0	0
Other noncurrent assets	[2]	28	31
Total noncurrent assets	[2]	28	31
Total assets	[2]	39	41
Long-term debt due within one year	[2]	32	35
Accounts payable	[2]	0	0
Accrued expenses	[2]	1	1
Unamortized energy contract liabilities	[2]	0	0
Other	[2]	0	0
Total current liabilities	[2]	33	36
Long-term debt	[2]	62	66
Asset retirement obligations	[2]	0	0
Unamortized energy contract liabilities	[2]	0	0
Other noncurrent liabilities	[2]	0	0
Total noncurrent liabilities	[2]	62	66
Total liabilities	[2]	95	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		10	2	54	101
Restricted cash		7	6	$ 7	$ 9
Accounts receivable, net
Customer		97	92
Other		51	56
Inventory
Other current assets		4	2
Total current assets		263	258
Property, plant and equipment, net		2,767	2,706
Other noncurrent assets		43	45
Total assets	[5]	3,530	3,445
Long-term debt due within one year		278	281
Accounts payable		166	118
Accrued expenses		41	33
Other		7	8
Total current liabilities		703	619
Long-term debt		836	840
Other noncurrent liabilities		24	25
Total liabilities	[5]	2,489	2,402
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash		7	6
Accounts receivable, net
Customer		0	0
Other		0	0
Inventory
Materials and supplies		0	0
Other current assets		0	0
Total current assets		7	6
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Other noncurrent assets		20	23
Total noncurrent assets		20	23
Total assets		27	29
Long-term debt due within one year		28	31
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		29	32
Long-term debt		54	58
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other noncurrent liabilities		0	0
Total noncurrent liabilities		54	58
Total liabilities		$ 83	$ 90

[1] Exelon’s consolidated assets include $9,727 million and $9,597 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,556 million and $3,618 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 — Variable Interest Entities.

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

[3] Generation’s consolidated assets include $9,688 million and $9,556 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,461 million and $3,516 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 — Variable Interest Entities.

[4] PHI’s consolidated total assets include $39 million and $41 million at March 31, 2018 and December 31, 2017, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $95 million and $102 million at March 31, 2018 and December 31, 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 3 — Variable Interest Entities.

[5] ACE’s consolidated total assets include $27 million and $29 million at March 31, 2018 and December 31, 2017, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $83 million and $90 million at March 31, 2018 and December 31, 2017, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 3 — Variable Interest Entities.