Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 6,502	$ 1,878	$ 1,609	$ 1,486
Customer		3,187	3,482
Other		912	1,227
Mark-to-market derivative assets		1,365	1,279
Materials and supplies		1,104	1,024
Other current assets		748	865
Total current assets		15,334	11,853
Property, plant and equipment, net		57,439	52,170
Nuclear decommissioning trust funds		10,342	10,537
Goodwill		2,672	2,672	2,625
Mark-to-market derivative assets		758	773
Other noncurrent assets		1,445	923
Total deferred debits and other assets		22,611	22,393
Total assets	[1]	95,384	86,416
Long-term debt due within one year		1,500	1,802
Accounts payable		2,883	3,048
Accrued expenses		2,376	1,539
Mark-to-market derivative liabilities		205	234
Energy Marketing Contract Liabilities, Current		100	238
Other current liabilities		842	931
Total current liabilities		9,118	8,762
Long-term debt		23,645	19,212
Asset retirement obligations		8,585	7,295
Pension obligations		3,385	3,366
Energy Marketing Contract Liabilities, Noncurrent		117	211
Other noncurrent liabilities		1,491	2,147
Total deferred credits and other liabilities		34,658	33,668
Total liabilities	[1]	68,062	62,283
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		164	392
Restricted cash		100	117
Customer		219	297
Other		43	57
Mark-to-market derivative assets		140	171
Materials and supplies		181	172
Other current assets		35	37
Total current assets		882	1,243
Property, plant and equipment, net		5,160	4,638
Nuclear decommissioning trust funds		2,036	2,097
Goodwill		47	47
Mark-to-market derivative assets		53	44
Other noncurrent assets		90	90
Total deferred debits and other assets		7,386	6,916
Total assets		8,268	8,159
Long-term debt due within one year		111	87
Accounts payable		216	292
Accrued expenses		115	111
Mark-to-market derivative liabilities		5	24
Energy Marketing Contract Liabilities, Current		12	22
Other current liabilities		13	25
Total current liabilities		472	561
Long-term debt		666	212
Asset retirement obligations		1,999	1,763
Pension obligations	[2]	9	9
Energy Marketing Contract Liabilities, Noncurrent		39	51
Other noncurrent liabilities		79	132
Total deferred credits and other liabilities		2,792	2,167
Total liabilities		3,264	2,728
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		431	780	1,258	671
Restricted cash		123	158
Customer		2,095	2,295
Other		360	318
Mark-to-market derivative assets		1,365	1,276
Materials and supplies		880	847
Other current assets		531	658
Total current assets		6,342	7,311
Property, plant and equipment, net		25,843	23,028
Nuclear decommissioning trust funds		10,342	10,537
Goodwill		47	47	0
Mark-to-market derivative assets		733	771
Other noncurrent assets		627	578
Total deferred debits and other assets		14,344	14,612
Total assets	[3]	46,529	44,951
Long-term debt due within one year		90	58
Accounts payable		1,583	1,759
Accrued expenses		935	886
Mark-to-market derivative liabilities		182	214
Energy Marketing Contract Liabilities, Current		100	238
Other current liabilities		356	413
Total current liabilities		4,933	4,459
Long-term debt		7,936	6,639
Asset retirement obligations		8,431	7,146
Energy Marketing Contract Liabilities, Noncurrent		117	211
Other noncurrent liabilities		602	719
Total deferred credits and other liabilities		19,757	18,859
Total liabilities	[3]	33,559	30,900
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		164	392
Restricted cash		77	96
Customer		219	297
Other		43	57
Mark-to-market derivative assets		140	171
Materials and supplies		181	172
Other current assets		30	30
Total current assets		854	1,215
Property, plant and equipment, net		5,160	4,638
Nuclear decommissioning trust funds		2,036	2,097
Goodwill		47	47
Mark-to-market derivative assets		53	44
Other noncurrent assets		85	77
Total deferred debits and other assets		7,381	6,903
Total assets		8,235	8,118
Long-term debt due within one year		27	5
Accounts payable		216	292
Accrued expenses		113	108
Mark-to-market derivative liabilities		5	24
Energy Marketing Contract Liabilities, Current		12	22
Other current liabilities		13	25
Total current liabilities		386	476
Long-term debt		623	81
Asset retirement obligations		1,999	1,763
Pension obligations	[2]	9	9
Energy Marketing Contract Liabilities, Noncurrent		39	51
Other noncurrent liabilities		79	132
Total deferred credits and other liabilities		2,749	2,036
Total liabilities		3,135	2,512
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		9	64	$ 31	$ 89
Customer		300	390
Other		112	82
Materials and supplies		33	30
Other current assets		3	5
Total current assets		845	951
Property, plant and equipment, net		6,597	6,204
Other noncurrent assets		8	9
Total deferred debits and other assets		853	901
Total assets	[4]	8,295	8,056
Long-term debt due within one year		378	75
Accounts payable		209	215
Accrued expenses		110	131
Other current liabilities		35	51
Total current liabilities		1,134	794
Long-term debt		1,480	1,857
Asset retirement obligations		17	17
Other noncurrent liabilities		61	60
Total deferred credits and other liabilities		2,552	2,400
Total liabilities	[4]	5,418	5,303
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		23	21
Customer		0	0
Other		0	0
Mark-to-market derivative assets		0	0
Materials and supplies		0	0
Other current assets		0	0
Total current assets		23	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 deferred debits and other assets		3	3
Total assets		26	24
Long-term debt due within one year		79	75
Accounts payable		0	0
Accrued expenses		2	2
Mark-to-market derivative liabilities		0	0
Energy Marketing Contract Liabilities, Current		0	0
Other current liabilities		0	0
Total current liabilities		81	77
Long-term debt		41	120
Asset retirement obligations		0	0
Pension obligations	[2]	0	0
Energy Marketing Contract Liabilities, Noncurrent		0	0
Other noncurrent liabilities		0	0
Total deferred credits and other liabilities		41	120
Total liabilities		$ 122	$ 197

[1] Exelon’s consolidated assets include $8,268 million and $8,159 million at December 31, 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 $3,264 million and $2,728 million at December 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.

[2] Includes the 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 17—Retirement Benefits for additional details

[3] Generation’s consolidated assets include $8,235 million and $8,118 million at December 31, 2015 and 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,135 million and $2,512 million at December 31, 2015 and 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.

[4] BGE’s consolidated assets include $26 million and $24 million at December 31, 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 $122 million and $197 million at December 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 2 - Variable Interest Entities.