Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Variable Interest Entity [Line Items]
Total assets	$ 344	[1]	$ 597	[1]
Total liabilities	79	[1]	286	[1]
Exelon's ownership interest in VIE	9	[1]	9	[1]
Other ownership interests in VIE	256	[1]	302	[1]
Assets Held-in-trust, Noncurrent	308		319
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	259	[1]	506	[1]
Total liabilities	32	[1]	237	[1]
Exelon's ownership interest in VIE	0	[1]	0	[1]
Other ownership interests in VIE	227	[1]	269	[1]
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	85	[1]	91	[1]
Total liabilities	47	[1]	49	[1]
Exelon's ownership interest in VIE	9	[1]	9	[1]
Other ownership interests in VIE	29	[1]	33	[1]
Investments [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	13
Investments [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss			13
Investments [Member] | Maximum [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	0		0
Investments [Member] | Maximum [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	13		13
Contract Intangible Asset [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	9		9
Contract Intangible Asset [Member] | Maximum [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	9		9
Payment Guarantee [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	3
Payment Guarantee [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss			3
Payment Guarantee [Member] | Maximum [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	3		3
Asset Held In Trust Noncurrent [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	27	[2]	27	[2]
Asset Held In Trust Noncurrent [Member] | Maximum [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	27	[2]	27	[2]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Assets Held-in-trust, Noncurrent	308		319
Payable to Zion Solutions	$ 281	[3]	$ 292	[3]

[1] These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.

[2] These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning include, gross pledged assets of $308 million and $319 million as of March 31, 2015 and December 31, 2014, respectively; offset by payables to ZionSolutions, LLC of $281 million and $292 million as of March 31, 2015 and December 31, 2014, respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE.

[3] Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized.