Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 694	$ 898	$ 536	$ 635
Restricted cash		206	207	252	253
Accounts receivable, net
Customer		4,094	4,445
Other		1,407	1,132
Inventory, net
Materials and Supplies		1,320	1,311
Other current assets		1,360	1,260
Total current assets		11,489	11,896
Property, plant and equipment, net		75,284	74,202
Nuclear decommissioning trust funds		13,110	13,272
Goodwill		6,677	6,677
Mark-to-market derivative assets		457	337
Other noncurrent assets		1,194	1,330
Total assets	[1]	117,249	116,770
Long-term debt due within one year		1,158	2,088
Accounts payable		3,113	3,532
Accrued expenses		1,665	1,837
Unamortized energy contract liabilities		171	231
Other		973	982
Total current liabilities		9,626	10,798
Long-term debt		33,179	32,176
Asset retirement obligations		10,222	10,029
Pension obligation		3,412	3,736
Unamortized energy contract liabilities		538	609
Other noncurrent liabilities		2,087	2,097
Total liabilities	[1]	84,410	84,583
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	205	126
Restricted cash	[2]	77	64
Accounts receivable, net
Customer	[2]	149	170
Other	[2]	32	25
Inventory, net
Materials and Supplies	[2]	208	205
Other current assets	[2]	47	45
Total current assets	[2]	718	635
Property, plant and equipment, net	[2]	6,157	6,186
Nuclear decommissioning trust funds	[2]	2,483	2,502
Other noncurrent assets	[2]	254	274
Total noncurrent assets	[2]	8,894	8,962
Total assets	[2]	9,612	9,597
Long-term debt due within one year	[2]	95	102
Accounts payable	[2]	74	114
Accrued expenses	[2]	81	67
Unamortized energy contract liabilities	[2]	16	18
Other	[2]	2	7
Total current liabilities	[2]	268	308
Long-term debt	[2]	1,119	1,154
Asset retirement obligations	[2]	2,088	2,035
Other noncurrent liabilities	[2]	69	121
Total noncurrent liabilities	[2]	3,276	3,310
Total liabilities	[2]	3,544	3,618
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		420	416	265	290
Restricted cash		130	138	166	158
Accounts receivable, net
Customer		2,435	2,697
Other		276	321
Inventory, net
Materials and Supplies		953	937
Other current assets		1,148	933
Total current assets		6,567	6,882
Property, plant and equipment, net		24,479	24,906
Nuclear decommissioning trust funds		13,110	13,272
Goodwill		47	47
Mark-to-market derivative assets		457	334
Other noncurrent assets		679	670
Total assets	[3]	47,668	48,457
Long-term debt due within one year		321	346
Accounts payable		1,264	1,773
Accrued expenses		976	1,022
Unamortized energy contract liabilities		36	43
Other		295	265
Total current liabilities		3,522	4,191
Long-term debt		7,661	7,734
Asset retirement obligations		10,037	9,844
Unamortized energy contract liabilities		34	48
Other noncurrent liabilities		648	658
Total liabilities	[3]	31,729	32,498
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		205	126
Restricted cash		72	58
Accounts receivable, net
Customer		149	170
Other		32	25
Inventory, net
Materials and Supplies		208	205
Other current assets		43	41
Total current assets		709	625
Property, plant and equipment, net		6,157	6,186
Nuclear decommissioning trust funds		2,483	2,502
Other noncurrent assets		226	243
Total noncurrent assets		8,866	8,931
Total assets		9,575	9,556
Long-term debt due within one year		66	67
Accounts payable		74	114
Accrued expenses		80	66
Unamortized energy contract liabilities		16	18
Other		2	7
Total current liabilities		238	272
Long-term debt		1,061	1,088
Asset retirement obligations		2,088	2,035
Other noncurrent liabilities		69	121
Total noncurrent liabilities		3,218	3,244
Total liabilities		3,456	3,516
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		7	17	12	23
Restricted cash		1	1	6	24
Accounts receivable, net
Customer		300	375
Other		89	94
Inventory, net
Materials and Supplies		45	40
Other current assets		4	3
Total current assets		658	811
Property, plant and equipment, net		7,864	7,602
Other noncurrent assets		6	4
Total assets		9,241	9,104
Accounts payable		249	265
Accrued expenses		95	164
Other		23	24
Total current liabilities		777	760
Long-term debt		2,578	2,577
Asset retirement obligations		23	23
Other noncurrent liabilities		73	56
Total liabilities		6,026	5,963
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		195	30	151	170
Restricted cash		38	42	40	43
Accounts receivable, net
Customer		495	486
Other		201	206
Inventory, net
Materials and Supplies		145	151
Other current assets		81	75
Total current assets		1,672	1,551
Property, plant and equipment, net		12,929	12,498
Goodwill		4,005	4,005
Other noncurrent assets		70	70
Total assets	[4]	21,766	21,247
Long-term debt due within one year		379	396
Accounts payable		514	348
Accrued expenses		220	261
Unamortized energy contract liabilities		134	188
Other		57	81
Total current liabilities		1,926	1,931
Long-term debt		5,737	5,478
Asset retirement obligations		16	16
Unamortized energy contract liabilities		504	561
Other noncurrent liabilities		403	389
Total liabilities	[4]	12,666	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]	5	6
Accounts receivable, net
Customer	[2]	0	0
Other	[2]	0	0
Inventory, net
Materials and Supplies	[2]	0	0
Other current assets	[2]	4	4
Total current assets	[2]	9	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]	37	41
Long-term debt due within one year	[2]	29	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]	30	36
Long-term debt	[2]	58	66
Asset retirement obligations	[2]	0	0
Other noncurrent liabilities	[2]	0	0
Total noncurrent liabilities	[2]	58	66
Total liabilities	[2]	88	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		6	2	7	101
Restricted cash		5	6	$ 7	$ 9
Accounts receivable, net
Customer		103	92
Other		50	56
Inventory, net
Other current assets		7	2
Total current assets		292	258
Property, plant and equipment, net		2,831	2,706
Other noncurrent assets		42	45
Total assets	[5]	3,619	3,445
Long-term debt due within one year		275	281
Accounts payable		143	118
Accrued expenses		35	33
Other		9	8
Total current liabilities		789	619
Long-term debt		832	840
Other noncurrent liabilities		26	25
Total liabilities	[5]	2,580	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		5	6
Accounts receivable, net
Customer		0	0
Other		0	0
Inventory, net
Materials and Supplies		0	0
Other current assets		0	0
Total current assets		5	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		25	29
Long-term debt due within one year		25	31
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		26	32
Long-term debt		50	58
Asset retirement obligations		0	0
Other noncurrent liabilities		0	0
Total noncurrent liabilities		50	58
Total liabilities		$ 76	$ 90

[1] Exelon’s consolidated assets include $9,612 million and $9,597 million at June 30, 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 $3,544 million and $3,618 million at June 30, 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 for additional information.

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

[3] Generation’s consolidated assets include $9,575 million and $9,556 million at June 30, 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 $3,456 million and $3,516 million at June 30, 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 for additional information.

[4] PHI’s consolidated total assets include $37 million and $41 million at June 30, 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 $88 million and $102 million at June 30, 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 for additional information.

[5] ACE’s consolidated total assets include $25 million and $29 million at June 30, 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 $76 million and $90 million at June 30, 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 for additional information.