Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2014 Variable Interest Entity, Primary Beneficiary [Member]		Apr. 01, 2014 Variable Interest Entity, Primary Beneficiary [Member]	Dec. 31, 2013 Variable Interest Entity, Primary Beneficiary [Member]		Sep. 30, 2014 Exelon Generation Co L L C [Member]		Dec. 31, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member] Variable Interest Entity, Primary Beneficiary [Member]		Dec. 31, 2013 Exelon Generation Co L L C [Member] Variable Interest Entity, Primary Beneficiary [Member]		Sep. 30, 2014 Baltimore Gas and Electric Company [Member]		Dec. 31, 2013 Baltimore Gas and Electric Company [Member]		Sep. 30, 2013 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Baltimore Gas and Electric Company [Member] Variable Interest Entity, Primary Beneficiary [Member]		Dec. 31, 2013 Baltimore Gas and Electric Company [Member] Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 2,763		$ 1,609		$ 1,644	$ 1,486	$ 372			$ 62		$ 1,311		$ 1,258		$ 928	$ 671	$ 372		$ 62		$ 27		$ 31		$ 7	$ 89	$ 0		$ 0
Restricted cash	318		167				142			80		187		71				95		52		65		28				47		28
Accounts receivable, net
Customer	2,815		2,981				213			260		1,705		1,689				213		260		366		480				0		0
Other	898		1,175				53			0		325		353				53		0		90		114				0		0
Mark-to-market derivative assets (current assets)	744		727				40			21		744		727				40		21								0		0
Inventory
Materials and supplies	1,045		829				171			0		865		671				171		0		34		28				0		0
Other current assets	1,022		652				53			34		821		491				47		23		6		7				0		0
Total current assets	11,837		10,137				1,044			457		7,458		6,439				991		418		869		1,011				47		28
Property, plant and equipment, net	51,630		47,330				4,517			1,171		23,143		20,111				4,517		1,171		6,126		5,864				0		0
Nuclear decommissioning trust funds	10,349		8,071				2,034			0		10,349		8,071				2,034		0								0		0
Goodwill	2,672		2,625				46			0		47		0				46		0								0		0
Other noncurrent assets	1,139		964				132			127		714		645				115		106		26		26				3		3
Total noncurrent assets							6,729			1,298								6,712		1,277								3		3
Total assets	85,264		79,924		79,924		7,773		6,000	1,755		45,019		41,232				7,703		1,695		7,915		7,861				50		31
Short-term borrowings	562		341				1			0		14		22				1		0		20		135				0		0
Long-term debt due within one year	2,064		1,509				83			85		73		561				5		5		72		70				72		70
Accounts payable	2,502		2,484				264			170		1,318		1,322				264		170		207		270				0		0
Accrued expenses	1,462		1,633				78			26		840		976				72		22		167		111				7		4
Mark-to-market derivative liabilities (current liabilities)	249		159				18			29		235		142				18		29								0		0
Other current liabilities	195		261				53			10		192		249				53		10								0		0
Total current liabilities	8,431		7,728				497			320		3,835		3,867				413		236		757		827				79		74
Long-term debt	19,200		17,623				256			298		6,741		5,645				84		86		1,904		1,941				158		195
Asset retirement obligations	7,003		5,194				1,654			0		6,853		5,047				1,654		0		18		19				0		0
Pension obligation(a)	1,809		1,876				8	[1]		0	[1]							8	[1]	0	[1]							0	[1]	0	[1]
Other noncurrent liabilities	2,104		2,540				179			40		718		811				179		40		60		67				0		0
Total deferred credits and other liabilities	31,935		30,985				2,097			338		19,171		17,455				1,925		126		2,295		2,280				158		195
Total liabilities	$ 60,214	[2]	$ 56,984	[2]			$ 2,594		$ 2,000	$ 658		$ 30,693	[3]	$ 28,490	[3]			$ 2,338		$ 362		$ 5,214	[4]	$ 5,306	[4]			$ 237		$ 269

[1] 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 — 13 - Retirement Benefits for additional details.

[2] Exelon’s consolidated assets include $7,773 million and $1,755 million at September 30, 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 $2,594 million and $658 million at September 30, 2014 and December 31, 2013, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 - Variable Interest Entities.

[3] Generation’s consolidated assets include $7,703 million and $1,695 million at September 30, 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 $2,338 million and $362 million at September 30, 2014 and December 31, 2013, 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 $50 million and $31 million at September 30, 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 $237 million and $269 million at September 30, 2014 and December 31, 2013, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 3 - Variable Interest Entities.