Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 7,265	$ 1,878	$ 2,763	$ 1,609
Restricted cash		341	271
Accounts receivable, net
Customer		3,215	3,482
Other		1,107	1,227
Inventory
Materials and supplies		1,074	1,024
Other current assets		1,178	865
Mark-to-market derivative assets (current assets)		1,116	1,279
Total current assets		16,867	12,097
Property, plant and equipment, net		55,814	52,087
Nuclear decommissioning trust funds		10,103	10,537
Goodwill		2,672	2,672
Mark-to-market derivative assets		801	773
Other noncurrent assets		1,499	1,160
Total assets		95,128	86,814
Short-term borrowings		675	460
Long-term debt due within one year		897	1,802
Accounts payable		2,987	3,048
Accrued expenses		1,576	1,539
Mark-to-market derivative liabilities (current liabilities)		204	234
Other current liabilities		118	238
Other Liabilities, Current		1,017	1,123
Total current liabilities		7,847	8,762
Long-term debt		24,541	19,362
Asset retirement obligations		8,405	7,295
Pension obligation(a)		3,014	3,366
Energy Marketing Contract Liabilities, Noncurrent		136	211
Other noncurrent liabilities		2,231	2,147
Total deferred credits and other liabilities		34,803	33,909
Total liabilities	[1]	67,839	62,681
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		330	392
Restricted cash		193	117
Accounts receivable, net
Customer		186	297
Other		32	57
Inventory
Materials and supplies		180	172
Other current assets		48	33
Mark-to-market derivative assets (current assets)		116	171
Total current assets		1,085	1,239
Property, plant and equipment, net		4,932	4,638
Nuclear decommissioning trust funds		1,973	2,097
Goodwill		47	47
Mark-to-market derivative assets		53	44
Other noncurrent assets		100	95
Total noncurrent assets		7,105	6,921
Total assets		8,190	8,160
Long-term debt due within one year		108	87
Accounts payable		266	292
Accrued expenses		92	111
Mark-to-market derivative liabilities (current liabilities)		0	24
Other current liabilities		10	22
Other Liabilities, Current		15	25
Total current liabilities		491	561
Long-term debt		729	212
Asset retirement obligations		1,906	1,763
Pension obligation(a)	[2]	9	9
Energy Marketing Contract Liabilities, Noncurrent		42	51
Other noncurrent liabilities		65	127
Total deferred credits and other liabilities		2,751	2,162
Total liabilities		3,242	2,723
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		545	780	1,311	1,258
Restricted cash		242	158
Accounts receivable, net
Customer		2,056	2,295
Other		487	318
Inventory
Materials and supplies		863	847
Other current assets		960	658
Mark-to-market derivative assets (current assets)		1,116	1,276
Total current assets		7,050	7,638
Property, plant and equipment, net		24,982	22,945
Nuclear decommissioning trust funds		10,103	10,537
Goodwill		47	47
Mark-to-market derivative assets		764	771
Other noncurrent assets		881	731
Total assets	[3]	46,479	45,348
Short-term borrowings		21	36
Long-term debt due within one year		97	58
Accounts payable		1,676	1,759
Accrued expenses		835	886
Mark-to-market derivative liabilities (current liabilities)		182	214
Other current liabilities		118	238
Other Liabilities, Current		546	605
Total current liabilities		4,786	4,459
Long-term debt		7,964	6,709
Asset retirement obligations		8,254	7,146
Energy Marketing Contract Liabilities, Noncurrent		136	211
Other noncurrent liabilities		727	719
Total deferred credits and other liabilities		19,870	19,186
Total liabilities	[3]	33,555	31,297
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		330	392
Restricted cash		146	96
Accounts receivable, net
Customer		186	297
Other		32	57
Inventory
Materials and supplies		180	172
Other current assets		43	26
Mark-to-market derivative assets (current assets)		116	171
Total current assets		1,033	1,211
Property, plant and equipment, net		4,932	4,638
Nuclear decommissioning trust funds		1,973	2,097
Goodwill		47	47
Mark-to-market derivative assets		53	44
Other noncurrent assets		92	82
Total noncurrent assets		7,097	6,908
Total assets		8,130	8,119
Long-term debt due within one year		26	5
Accounts payable		266	292
Accrued expenses		88	108
Mark-to-market derivative liabilities (current liabilities)		0	24
Other current liabilities		10	22
Other Liabilities, Current		15	25
Total current liabilities		405	476
Long-term debt		643	81
Asset retirement obligations		1,906	1,763
Pension obligation(a)	[2]	9	9
Energy Marketing Contract Liabilities, Noncurrent		42	51
Other noncurrent liabilities		65	127
Total deferred credits and other liabilities		2,665	2,031
Total liabilities		3,070	2,507
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		27	64	$ 27	$ 31
Restricted cash		48	50
Accounts receivable, net
Customer		318	390
Other		77	82
Inventory
Materials and supplies		35	30
Other current assets		5	5
Total current assets		822	957
Property, plant and equipment, net		6,459	6,204
Other noncurrent assets		25	25
Total assets	[4]	8,134	8,078
Short-term borrowings		50	120
Long-term debt due within one year		77	75
Accounts payable		201	215
Accrued expenses		159	131
Other Liabilities, Current		32	51
Total current liabilities		797	846
Long-term debt		1,828	1,867
Asset retirement obligations		15	17
Other noncurrent liabilities		59	60
Total deferred credits and other liabilities		2,406	2,354
Total liabilities	[4]	5,289	5,325
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash		46	21
Accounts receivable, net
Customer		0	0
Other		0	0
Inventory
Materials and supplies		0	0
Other current assets		0	0
Mark-to-market derivative assets (current assets)		0	0
Total current assets		46	21
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		3	3
Total noncurrent assets		3	3
Total assets		49	24
Long-term debt due within one year		77	75
Accounts payable		0	0
Accrued expenses		4	2
Mark-to-market derivative liabilities (current liabilities)		0	0
Other current liabilities		0	0
Other Liabilities, Current		0	0
Total current liabilities		81	77
Long-term debt		81	120
Asset retirement obligations		0	0
Pension obligation(a)		0	0
Energy Marketing Contract Liabilities, Noncurrent		0	0
Other noncurrent liabilities		0	0
Total deferred credits and other liabilities		81	120
Total liabilities		$ 162	$ 197

[1] Exelon’s consolidated assets include $8,190 million and $8,160 million at September 30, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,242 million and $2,723 million at September 30, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 — Variable Interest Entities.

[2] Includes 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 14 — Retirement Benefits for additional details.

[3] Generation’s consolidated assets include $8,130 million and $8,119 million at September 30, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,070 million and $2,507 million at September 30, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 — Variable Interest Entities.

[4] BGE’s consolidated assets include $49 million and $24 million at September 30, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $162 million and $197 million at September 30, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 3 — Variable Interest Entities.