Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 1,825		$ 1,878		$ 914	$ 1,609
Restricted cash	297		271
Accounts receivable, net
Customer	3,702		3,482
Other	1,077		1,227
Inventory
Materials and supplies	1,035		1,024
Other current assets	793		865
Mark-to-market derivative assets (current assets)	1,117		1,279
Total current assets	11,357		12,097
Property, plant and equipment, net	53,001		52,087
Nuclear decommissioning trust funds	10,712		10,537
Goodwill	2,672		2,672
Mark-to-market derivative assets	913		773
Other noncurrent assets	1,234		1,160
Total assets	87,391		86,814		86,814
Short-term borrowings	309		460
Long-term debt due within one year	1,260		1,802
Accounts payable	2,839		3,048
Accrued expenses	1,230		1,539
Mark-to-market derivative liabilities (current liabilities)	117		234
Other current liabilities	172		238
Other	1,018		1,123
Total current liabilities	7,374		8,762
Long-term debt	20,519		19,362
Asset retirement obligations	7,446		7,295
Pension obligation(a)	3,154		3,366
Energy Marketing Contract Liabilities, Noncurrent	189		211
Other noncurrent liabilities	2,166		2,147
Total deferred credits and other liabilities	34,212		33,909
Total liabilities	62,753	[1]	62,681	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	334		392
Restricted cash	159		117
Accounts receivable, net
Customer	296		297
Other	33		57
Inventory
Materials and supplies	168		172
Other current assets	40		33
Mark-to-market derivative assets (current assets)	130		171
Total current assets	1,160		1,239
Property, plant and equipment, net	4,720		4,638
Nuclear decommissioning trust funds	2,114		2,097
Goodwill	47		47
Mark-to-market derivative assets	51		44
Other noncurrent assets	90		95
Total noncurrent assets	7,022		6,921
Total assets	8,182		8,160
Long-term debt due within one year	85		87
Accounts payable	268		292
Accrued expenses	77		111
Mark-to-market derivative liabilities (current liabilities)	10		24
Other current liabilities	9		22
Other	18		25
Total current liabilities	467		561
Long-term debt	211		212
Asset retirement obligations	1,843		1,763
Pension obligation(a)	9	[2]	9	[2]
Energy Marketing Contract Liabilities, Noncurrent	48		51
Other noncurrent liabilities	124		127
Total deferred credits and other liabilities	2,235		2,162
Total liabilities	2,702		2,723
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	532		780		566	1,258
Restricted cash	179		158
Accounts receivable, net
Customer	2,320		2,295
Other	378		318
Inventory
Materials and supplies	841		847
Other current assets	530		658
Mark-to-market derivative assets (current assets)	1,116		1,276
Total current assets	6,719		7,638
Property, plant and equipment, net	23,414		22,945
Nuclear decommissioning trust funds	10,712		10,537
Goodwill	47		47
Mark-to-market derivative assets	911		771
Other noncurrent assets	776		731
Total assets	45,318	[3]	45,348	[3]
Short-term borrowings	25		36
Long-term debt due within one year	75		58
Accounts payable	1,634		1,759
Accrued expenses	694		886
Mark-to-market derivative liabilities (current liabilities)	97		214
Other current liabilities	172		238
Other	532		605
Total current liabilities	4,275		4,459
Long-term debt	7,477		6,709
Asset retirement obligations	7,296		7,146
Energy Marketing Contract Liabilities, Noncurrent	189		211
Other noncurrent liabilities	764		719
Total deferred credits and other liabilities	19,458		19,186
Total liabilities	32,150	[3]	31,297	[3]
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	334		392
Restricted cash	113		96
Accounts receivable, net
Customer	296		297
Other	33		57
Inventory
Materials and supplies	168		172
Other current assets	34		26
Mark-to-market derivative assets (current assets)	130		171
Total current assets	1,108		1,211
Property, plant and equipment, net	4,720		4,638
Nuclear decommissioning trust funds	2,114		2,097
Goodwill	47		47
Mark-to-market derivative assets	51		44
Other noncurrent assets	78		82
Total noncurrent assets	7,010		6,908
Total assets	8,118		8,119
Long-term debt due within one year	5		5
Accounts payable	268		292
Accrued expenses	71		108
Mark-to-market derivative liabilities (current liabilities)	10		24
Other current liabilities	9		22
Other	18		25
Total current liabilities	381		476
Long-term debt	81		81
Asset retirement obligations	1,843		1,763
Pension obligation(a)	9	[2]	9	[2]
Energy Marketing Contract Liabilities, Noncurrent	48		51
Other noncurrent liabilities	124		127
Total deferred credits and other liabilities	2,105		2,031
Total liabilities	2,486		2,507
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	41		64		23
Restricted cash	48		50
Accounts receivable, net
Customer	489		390
Other	99		82
Inventory
Materials and supplies	33		30
Other current assets	4		5
Total current assets	962		957
Property, plant and equipment, net	6,280		6,204
Other noncurrent assets	28		25
Total assets	8,130		8,078
Short-term borrowings	0		120
Long-term debt due within one year	75		75
Accounts payable	222		215
Accrued expenses	155		131
Other	27		51
Total current liabilities	780		846
Long-term debt	1,867		1,867
Asset retirement obligations	18		17
Other noncurrent liabilities	62		60
Total deferred credits and other liabilities	2,402		2,354
Total liabilities	5,307	[4]	5,325	[4]
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	75		75
Accounts payable	0		0
Accrued expenses	5		2
Mark-to-market derivative liabilities (current liabilities)	0		0
Other current liabilities	0		0
Other	0		0
Total current liabilities	80		77
Long-term debt	120		120
Asset retirement obligations	0		0
Pension obligation(a)	0	[2]	0	[2]
Energy Marketing Contract Liabilities, Noncurrent	0		0
Other noncurrent liabilities	0		0
Total deferred credits and other liabilities	120		120
Total liabilities	$ 200		$ 197

[1] Exelon’s consolidated assets include $8,182 million and $8,160 million at March 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 $2,702 million and $2,723 million at March 31, 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 12 — Retirement Benefits for additional details.

[3] Generation’s consolidated assets include $8,118 million and $8,119 million at March 31, 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 $2,486 million and $2,507 million at March 31, 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 March 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 $200 million and $197 million at March 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 3 — Variable Interest Entities.