Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,918	$ 898	$ 1,203	$ 635
Restricted cash		240	207	320	253
Accounts receivable, net
Customer		4,239	4,445
Other		1,246	1,132
Inventory, net
Materials and Supplies		1,316	1,311
Other current assets		1,177	1,260
Total current assets		13,473	11,896
Property, plant and equipment, net		75,840	74,202
Nuclear decommissioning trust funds		12,464	13,272
Goodwill		6,677	6,677
Mark-to-market derivative assets		449	337
Other noncurrent assets		1,560	1,330
Total assets	[1]	119,485	116,770
Long-term debt due within one year		771	2,088
Accounts payable		3,348	3,532
Accrued expenses		1,964	1,837
Unamortized energy contract liabilities		158	231
Other		935	982
Total current liabilities		10,140	10,798
Long-term debt		34,519	32,176
Asset retirement obligations		9,747	10,029
Pension obligation		3,385	3,736
Unamortized energy contract liabilities		497	609
Other noncurrent liabilities		2,160	2,097
Total liabilities	[1]	86,097	84,583
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	316	126
Restricted cash	[2]	77	64
Accounts receivable, net
Customer	[2]	165	170
Other	[2]	30	25
Inventory, net
Materials and Supplies	[2]	214	205
Other current assets	[2]	65	45
Total current assets	[2]	867	635
Property, plant and equipment, net	[2]	6,158	6,186
Nuclear decommissioning trust funds	[2]	2,523	2,502
Other noncurrent assets	[2]	256	274
Total noncurrent assets	[2]	8,937	8,962
Total assets	[2]	9,804	9,597
Long-term debt due within one year	[2]	97	102
Accounts payable	[2]	128	114
Accrued expenses	[2]	73	67
Unamortized energy contract liabilities	[2]	16	18
Other	[2]	14	7
Total current liabilities	[2]	328	308
Long-term debt	[2]	1,087	1,154
Asset retirement obligations	[2]	2,116	2,035
Other noncurrent liabilities	[2]	75	121
Total noncurrent liabilities	[2]	3,278	3,310
Total liabilities	[2]	3,606	3,618
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		1,187	416	360	290
Restricted cash		152	138	186	158
Accounts receivable, net
Customer		2,545	2,697
Other		278	321
Inventory, net
Materials and Supplies		948	937
Other current assets		854	933
Total current assets		8,049	6,882
Property, plant and equipment, net		24,168	24,906
Nuclear decommissioning trust funds		12,464	13,272
Goodwill		47	47
Mark-to-market derivative assets		449	334
Other noncurrent assets		730	670
Total assets	[3]	48,207	48,457
Long-term debt due within one year		336	346
Accounts payable		1,450	1,773
Accrued expenses		1,200	1,022
Unamortized energy contract liabilities		33	43
Other		255	265
Total current liabilities		4,767	4,191
Long-term debt		7,605	7,734
Asset retirement obligations		9,521	9,844
Unamortized energy contract liabilities		23	48
Other noncurrent liabilities		635	658
Total liabilities	[3]	32,247	32,498
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		316	126
Restricted cash		70	58
Accounts receivable, net
Customer		165	170
Other		30	25
Inventory, net
Materials and Supplies		214	205
Other current assets		62	41
Total current assets		857	625
Property, plant and equipment, net		6,158	6,186
Nuclear decommissioning trust funds		2,523	2,502
Other noncurrent assets		230	243
Total noncurrent assets		8,911	8,931
Total assets		9,768	9,556
Long-term debt due within one year		72	67
Accounts payable		128	114
Accrued expenses		72	66
Unamortized energy contract liabilities		16	18
Other		14	7
Total current liabilities		302	272
Long-term debt		1,035	1,088
Asset retirement obligations		2,116	2,035
Other noncurrent liabilities		75	121
Total noncurrent liabilities		3,226	3,244
Total liabilities		3,528	3,516
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		113	17	29	23
Restricted cash		3	1	1	24
Accounts receivable, net
Customer		296	375
Other		96	94
Inventory, net
Materials and Supplies		39	40
Other current assets		10	3
Total current assets		798	811
Property, plant and equipment, net		8,039	7,602
Other noncurrent assets		7	4
Total assets		9,541	9,104
Accounts payable		277	265
Accrued expenses		146	164
Other		23	24
Total current liabilities		707	760
Long-term debt		2,876	2,577
Asset retirement obligations		24	23
Other noncurrent liabilities		75	56
Total liabilities		6,297	5,963
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		153	30	137	170
Restricted cash		42	42	43	43
Accounts receivable, net
Customer		500	486
Other		266	206
Inventory, net
Materials and Supplies		149	151
Other current assets		60	75
Total current assets		1,700	1,551
Property, plant and equipment, net		13,167	12,498
Goodwill		4,005	4,005
Other noncurrent assets		67	70
Total assets	[4]	21,957	21,247
Long-term debt due within one year		117	396
Accounts payable		505	348
Accrued expenses		269	261
Unamortized energy contract liabilities		125	188
Other		57	81
Total current liabilities		1,769	1,931
Long-term debt		5,972	5,478
Asset retirement obligations		53	16
Unamortized energy contract liabilities		474	561
Other noncurrent liabilities		395	389
Total liabilities	[4]	12,791	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, net
Materials and Supplies	[2]	0	0
Other current assets	[2]	3	4
Total current assets	[2]	10	10
Property, plant and equipment, net	[2]	0	0
Nuclear decommissioning trust funds	[2]	0	0
Other noncurrent assets	[2]	26	31
Total noncurrent assets	[2]	26	31
Total assets	[2]	36	41
Long-term debt due within one year	[2]	25	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]	26	36
Long-term debt	[2]	52	66
Asset retirement obligations	[2]	0	0
Other noncurrent liabilities	[2]	0	0
Total noncurrent liabilities	[2]	52	66
Total liabilities	[2]	78	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		11	2	5	101
Restricted cash		7	6	$ 9	$ 9
Accounts receivable, net
Customer		144	92
Other		59	56
Inventory, net
Other current assets		21	2
Total current assets		317	258
Property, plant and equipment, net		2,883	2,706
Other noncurrent assets		41	45
Total assets	[5]	3,694	3,445
Long-term debt due within one year		22	281
Accounts payable		149	118
Accrued expenses		38	33
Other		9	8
Total current liabilities		566	619
Long-term debt		1,078	840
Other noncurrent liabilities		26	25
Total liabilities	[5]	2,621	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, net
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		19	23
Total noncurrent assets		19	23
Total assets		26	29
Long-term debt due within one year		22	31
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		23	32
Long-term debt		45	58
Asset retirement obligations		0	0
Other noncurrent liabilities		0	0
Total noncurrent liabilities		45	58
Total liabilities		$ 68	$ 90

[1] Exelon’s consolidated assets include $9,804 million and $9,597 million at September 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 $3,606 million and $3,618 million at September 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 $9,768 million and $9,556 million at September 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 $3,528 million and $3,516 million at September 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 $36 million and $41 million at September 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 $78 million and $102 million at September 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 $26 million and $29 million at September 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 $68 million and $90 million at September 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.