Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016		Sep. 30, 2016	Mar. 23, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,203	$ 635		$ 1,897		$ 6,502
Restricted cash		320	253
Accounts receivable, net
Customer		3,854	4,158
Other		950	1,201
Mark-to-market derivatives assets		699	917
Inventory
Materials and supplies		1,281	1,274
Other current assets		1,435	930
Total current assets		12,724	12,412
Property, plant and equipment, net		73,067	71,555
Nuclear decommissioning trust funds		12,966	11,061
Goodwill		6,677	6,677
Mark-to-market derivative assets		426	492
Other noncurrent assets		1,277	1,472
Total assets		118,473	114,904
Long-term debt due within one year		3,164	2,430
Accounts payable		3,132	3,441
Accrued expenses		3,080	3,460
Mark-to-market derivative liabilities		178	282
Unamortized energy contract liabilities		283	407
Other		933	981
Total current liabilities		12,395	13,457
Long-term debt		31,701	31,575
Asset retirement obligations		9,733	9,111
Pension obligation(c)		4,055	4,248
Unamortized energy contract liabilities		656	830
Other noncurrent liabilities		1,899	1,827
Total liabilities	[1]	88,156	87,292
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	130	150	[3]
Restricted cash	[2]	85	59	[3]
Accounts receivable, net
Customer	[2]	139	371	[3]
Other	[2]	25	48	[3]
Mark-to-market derivatives assets	[2]	0	31	[3]
Inventory
Materials and supplies	[2]	196	199	[3]
Other current assets	[2]	56	50	[3]
Total current assets	[2]	631	908	[3]
Property, plant and equipment, net	[2]	6,213	5,415	[3]
Nuclear decommissioning trust funds	[2]	2,415	2,185	[3]
Goodwill	[2]	0	47	[3]
Mark-to-market derivative assets	[2]	0	23	[3]
Other noncurrent assets	[2]	261	315	[3]
Total noncurrent assets	[2]	8,889	7,985	[3]
Total assets	[2]	9,520	8,893	[3]
Long-term debt due within one year	[2]	182	181	[3]
Accounts payable	[2]	104	269	[3]
Accrued expenses	[2]	90	119	[3]
Mark-to-market derivative liabilities	[2]	0	60	[3]
Unamortized energy contract liabilities	[2]	17	15	[3]
Other	[2]	11	30	[3]
Total current liabilities	[2]	404	674	[3]
Long-term debt	[2]	1,172	641	[3]
Asset retirement obligations	[2]	2,009	1,904	[3]
Pension obligation(c)	[2],[4]	0	9	[3]
Unamortized energy contract liabilities	[2]	9	22	[3]
Other noncurrent liabilities	[2]	94	106	[3]
Total noncurrent liabilities	[2]	3,284	2,682	[3]
Total liabilities	[2]	3,688	3,356	[3]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		360	290		375		431
Restricted cash		186	158
Accounts receivable, net
Customer		2,339	2,433
Other		275	558
Mark-to-market derivatives assets		699	917
Inventory
Materials and supplies		917	935
Other current assets		1,157	701
Total current assets		6,439	6,528
Property, plant and equipment, net		24,793	25,585
Nuclear decommissioning trust funds		12,966	11,061
Goodwill		47	47
Mark-to-market derivative assets		416	476
Other noncurrent assets		648	688
Total assets		47,744	46,974
Long-term debt due within one year		1,659	1,117
Accounts payable		1,492	1,610
Accrued expenses		797	989
Mark-to-market derivative liabilities		158	263
Unamortized energy contract liabilities		52	72
Other		266	313
Total current liabilities		5,059	5,683
Long-term debt		6,956	7,202
Asset retirement obligations		9,548	8,922
Unamortized energy contract liabilities		57	80
Other noncurrent liabilities		632	595
Total liabilities	[5]	33,947	33,718
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		130	150
Restricted cash		76	27
Accounts receivable, net
Customer		139	371
Other		25	48
Mark-to-market derivatives assets		0	31
Inventory
Materials and supplies		196	199
Other current assets		52	44
Total current assets		618	870
Property, plant and equipment, net		6,213	5,415
Nuclear decommissioning trust funds		2,415	2,185
Goodwill		0	47
Mark-to-market derivative assets		0	23
Other noncurrent assets		231	277
Total noncurrent assets		8,859	7,947
Total assets		9,477	8,817
Long-term debt due within one year		146	99
Accounts payable		104	269
Accrued expenses		89	116
Mark-to-market derivative liabilities		0	60
Unamortized energy contract liabilities		17	15
Other		11	30
Total current liabilities		367	589
Long-term debt		1,097	540
Asset retirement obligations		2,009	1,904
Pension obligation(c)	[4]	0	9
Unamortized energy contract liabilities		9	22
Other noncurrent liabilities		94	106
Total noncurrent liabilities		3,209	2,581
Total liabilities		3,576	3,170
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		29	23		341		9
Restricted cash		1	24
Accounts receivable, net
Customer		288	395
Other		86	102
Inventory
Materials and supplies		40	38
Other current assets		4	7
Total current assets		702	842
Property, plant and equipment, net		7,418	7,040
Other noncurrent assets		4	9
Total assets	[6]	8,923	8,704
Long-term debt due within one year		0	41
Accounts payable		218	205
Accrued expenses		147	175
Other		28	26
Total current liabilities		612	707
Long-term debt		2,577	2,281
Asset retirement obligations		23	21
Other noncurrent liabilities		52	61
Total liabilities	[6]	5,915	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
Accounts receivable, net
Customer			0
Other			0
Mark-to-market derivatives assets			0
Inventory
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			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			0
Total current liabilities			42
Long-term debt			0
Asset retirement obligations			0
Pension obligation(c)	[4]		0
Unamortized energy contract liabilities			0
Other noncurrent liabilities			0
Total noncurrent liabilities			0
Total liabilities			42
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		137	170		299	$ 319
Restricted cash		43	43
Accounts receivable, net
Customer		490	496
Other		209	283
Mark-to-market derivatives assets		0	0
Inventory
Materials and supplies		141	116
Other current assets		59	71
Total current assets		1,656	1,838
Property, plant and equipment, net		12,219	11,598
Goodwill		4,005	4,005
Mark-to-market derivative assets		0	0
Other noncurrent assets		77	81
Total assets	[7]	21,301	21,025
Long-term debt due within one year		159	253
Accounts payable		397	458
Accrued expenses		294	272
Mark-to-market derivative liabilities		0	0
Unamortized energy contract liabilities		231	335
Other		41	47
Total current liabilities		1,557	2,284
Long-term debt		5,771	5,645
Asset retirement obligations		17	14
Unamortized energy contract liabilities		599	750
Other noncurrent liabilities		214	249
Total liabilities		12,435	13,009
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	0	0
Restricted cash	[2]	9	9
Accounts receivable, net
Customer	[2]	0	0
Other	[2]	0	0
Mark-to-market derivatives assets	[2]	0	0
Inventory
Materials and supplies	[2]	0	0
Other current assets	[2]	4	5
Total current assets	[2]	13	14
Property, plant and equipment, net	[2]	0	0
Nuclear decommissioning trust funds	[2]	0	0
Goodwill	[2]	0	0
Mark-to-market derivative assets	[2]	0	0
Other noncurrent assets	[2]	30	35
Total noncurrent assets	[2]	30	35
Total assets	[2]	43	49
Long-term debt due within one year	[2]	36	40
Accounts payable	[2]	0	0
Accrued expenses	[2]	1	2
Mark-to-market derivative liabilities	[2]	0	0
Unamortized energy contract liabilities	[2]	0	0
Other	[2]	0	0
Total current liabilities	[2]	37	42
Long-term debt	[2]	75	101
Asset retirement obligations	[2]	0	0
Pension obligation(c)	[2],[4]	0	0
Unamortized energy contract liabilities	[2]	0	0
Other noncurrent liabilities	[2]	0	0
Total noncurrent liabilities	[2]	75	101
Total liabilities	[2]	112	143
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		5	101		$ 165		$ 3
Restricted cash		9	9
Accounts receivable, net
Customer		107	125
Other		54	44
Inventory
Materials and supplies		29	22
Other current assets		3	2
Total current assets		309	399
Property, plant and equipment, net		2,662	2,521
Other noncurrent assets		42	44
Total assets	[8]	3,510	3,457
Long-term debt due within one year		32	35
Accounts payable		122	132
Accrued expenses		39	38
Other		6	8
Total current liabilities		345	320
Long-term debt		1,098	1,120
Other noncurrent liabilities		25	32
Total liabilities		2,452	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		9	9
Accounts receivable, net
Customer		0	0
Other		0	0
Mark-to-market derivatives assets		0	0
Inventory
Materials and supplies		0	0
Other current assets		0	0
Total current assets		9	9
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Goodwill		0	0
Mark-to-market derivative assets		0	0
Other noncurrent assets		22	23
Total noncurrent assets		22	23
Total assets		31	32
Long-term debt due within one year		32	35
Accounts payable		0	0
Accrued expenses		1	2
Mark-to-market derivative liabilities		0	0
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		33	37
Long-term debt		67	89
Asset retirement obligations		0	0
Pension obligation(c)	[4]	0	0
Unamortized energy contract liabilities		0	0
Other noncurrent liabilities		0	0
Total noncurrent liabilities		67	89
Total liabilities		$ 100	$ 126

[1] Exelon’s consolidated assets include $9,520 million and $8,893 million at September 30, 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 $3,688 million and $3,356 million at September 30, 2017 and December 31, 2016, 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] Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

[4] Includes the retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s Consolidated Balance Sheets. See Note 14 - Retirement Benefits for additional details.

[5] Generation’s consolidated assets include $9,477 million and $8,817 million at September 30, 2017 and December 31, 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,576 million and $3,170 million at September 30, 2017 and December 31, 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 - Variable Interest Entities.

[6] 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 September 30, 2017. See Note 3 - Variable Interest Entities.

[7] PHI’s consolidated total assets include $43 million and $49 million at September 30, 2017 and December 31, 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 $112 million and $143 million at September 30, 2017 and December 31, 2016, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 3 - Variable Interest Entities.

[8] ACE’s consolidated total assets include $31 million and $32 million at September 30, 2017 and December 31, 2016, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $100 million and $126 million at September 30, 2017 and December 31, 2016, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 3 - Variable Interest Entities.