Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 1,878		$ 1,609		$ 1,486	$ 1,016
Customer	3,482		2,981
Other	1,227		1,175
Mark-to-market derivative assets	1,279		727
Materials and supplies	1,024		829
Other current assets	865		652
Total current assets	12,097		10,137
Property, plant and equipment, net	52,087		47,330
Nuclear decommissioning trust funds	10,537		8,071
Goodwill	2,672		2,625
Mark-to-market derivative assets	773		607
Other noncurrent assets	1,160		964
Total deferred debits and other assets	22,630		22,457
Total assets	86,814	[1]	79,924	[1]
Long-term debt due within one year	1,802		1,509
Accounts payable	3,048		2,484
Accrued expenses	1,539		1,633
Mark-to-market derivative liabilities	234		159
Energy Marketing Contract Liabilities, Current	238		261
Other current liabilities	1,123		858
Total current liabilities	8,762		7,728
Long-term debt	19,362		17,623
Asset retirement obligations	7,295		5,194
Pension obligations	3,366		1,876
Energy Marketing Contract Liabilities, Noncurrent	211		266
Other noncurrent liabilities	2,147		2,540
Total deferred credits and other liabilities	33,909		30,985
Total liabilities	62,681	[1]	56,984	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	392		62
Restricted cash	117		80
Customer	297		260
Other	57		0
Mark-to-market derivative assets	171		21
Materials and supplies	172		0
Other current assets	33		34
Total current assets	1,239		457
Property, plant and equipment, net	4,638		1,171
Nuclear decommissioning trust funds	2,097		0
Goodwill	47		0
Mark-to-market derivative assets	44		0
Other noncurrent assets	95		127
Total deferred debits and other assets	6,921		1,298
Total assets	8,160		1,755
Long-term debt due within one year	87		85
Accounts payable	292		170
Accrued expenses	111		26
Mark-to-market derivative liabilities	24		29
Energy Marketing Contract Liabilities, Current	22		5
Other current liabilities	25		5
Total current liabilities	561		320
Long-term debt	212		298
Asset retirement obligations	1,763		0
Pension obligations	9	[2]	0	[2]
Energy Marketing Contract Liabilities, Noncurrent	51		28
Other noncurrent liabilities	127		12
Total deferred credits and other liabilities	2,162		338
Total liabilities	2,723		658
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	780		1,258		671	496
Restricted cash	158		71
Customer	2,295		1,689
Other	318		353
Mark-to-market derivative assets	1,276		727
Materials and supplies	847		671
Other current assets	658		491
Total current assets	7,638		6,439
Property, plant and equipment, net	22,945		20,111
Nuclear decommissioning trust funds	10,537		8,071
Goodwill	47		0
Mark-to-market derivative assets	771		600
Other noncurrent assets	731		645
Total deferred debits and other assets	14,765		14,682
Total assets	45,348	[3]	41,232	[3]
Long-term debt due within one year	58		561
Accounts payable	1,759		1,322
Accrued expenses	886		976
Mark-to-market derivative liabilities	214		142
Energy Marketing Contract Liabilities, Current	238		249
Other current liabilities	605		389
Total current liabilities	4,459		3,867
Long-term debt	6,709		5,645
Asset retirement obligations	7,146		5,047
Energy Marketing Contract Liabilities, Noncurrent	211		266
Other noncurrent liabilities	719		811
Total deferred credits and other liabilities	19,186		17,455
Total liabilities	31,297	[3]	28,490	[3]
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	392		62
Restricted cash	96		52
Customer	297		260
Other	57		0
Mark-to-market derivative assets	171		21
Materials and supplies	172		0
Other current assets	26		23
Total current assets	1,211		418
Property, plant and equipment, net	4,638		1,171
Nuclear decommissioning trust funds	2,097		0
Goodwill	47		0
Mark-to-market derivative assets	44		0
Other noncurrent assets	82		106
Total deferred debits and other assets	6,908		1,277
Total assets	8,119		1,695
Long-term debt due within one year	5		5
Accounts payable	292		170
Accrued expenses	108		22
Mark-to-market derivative liabilities	24		29
Energy Marketing Contract Liabilities, Current	22
Other current liabilities	25		5
Total current liabilities	476		236
Long-term debt	81		86
Asset retirement obligations	1,763		0
Pension obligations	9	[2]	0	[2]
Energy Marketing Contract Liabilities, Noncurrent	51		28
Other noncurrent liabilities	127		12
Total deferred credits and other liabilities	2,031		126
Total liabilities	2,507		362
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	64		31		89	49
Customer	390		480
Other	82		114
Materials and supplies	30		28
Other current assets	5		7
Total current assets	957		1,011
Property, plant and equipment, net	6,204		5,864
Other noncurrent assets	25		26
Total deferred debits and other assets	917		986
Total assets	8,078	[4]	7,861	[4]
Accounts payable	215		270
Accrued expenses	131		111
Other current liabilities	51		35
Total current liabilities	846		827
Long-term debt	1,867		1,941
Asset retirement obligations	17		19
Other noncurrent liabilities	60		67
Total deferred credits and other liabilities	2,354		2,280
Total liabilities	5,325	[4]	5,306	[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	21		28
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	21		28
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	24		31
Long-term debt due within one year	75		70
Accounts payable	0		0
Accrued expenses	2		4
Mark-to-market derivative liabilities	0		0
Energy Marketing Contract Liabilities, Current	0		0
Other current liabilities	0		0
Total current liabilities	77		74
Long-term debt	120		195
Asset retirement obligations	0		0
Pension obligations	0	[2]	0	[2]
Energy Marketing Contract Liabilities, Noncurrent	0		0
Other noncurrent liabilities	0		0
Total deferred credits and other liabilities	120		195
Total liabilities	$ 197		$ 269

[1] Exelon’s consolidated assets include $8,160 million and $1,755 million at December 31, 2014 and December 31, 2013, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $2,723 million and $658 million at December 31, 2014 and December 31, 2013, 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 16—Retirement Benefits for additional details

[3] Generation’s consolidated assets include $8,119 million and $1,695 million at December 31, 2014 and December 31, 2013, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $2,507 million and $362 million at December 31, 2014 and December 31, 2013, 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 $24 million and $31 million at December 31, 2014 and December 31, 2013, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $197 million and $269 million at December 31, 2014 and December 31, 2013, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 2 - Variable Interest Entities.