Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Variable Interest Entity [Line Items]
Total assets	$ 422	[1]	$ 460	[1]
Total liabilities	117	[1]	140	[1]
Exelon's ownership interest in VIE	62	[1]	86	[1]
Other ownership interests in VIE	243	[1]	234	[1]
Assets Held-in-trust, Noncurrent	365		458
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	115	[1]	128	[1]
Total liabilities	2	[1]	17	[1]
Exelon's ownership interest in VIE	0	[1]	0	[1]
Other ownership interests in VIE	113	[1]	111	[1]
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	307	[1]	332	[1]
Total liabilities	115	[1]	123	[1]
Exelon's ownership interest in VIE	62	[1]	86	[1]
Other ownership interests in VIE	130	[1]	123	[1]
Investments [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	66
Investments [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss			74
Investments [Member] | Maximum [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	0		7
Investments [Member] | Maximum [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	66		67
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			5
Payment Guarantee [Member] | Maximum [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	3		5
Asset Held In Trust Noncurrent [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	31	[2]	44	[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	31	[2]	44	[2]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Assets Held-in-trust, Noncurrent	365		458
Payable to Zion Solutions	$ 334	[3]	$ 414	[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 includes gross pledged assets of $365 million and $458 million as of September 30, 2014 and December 31, 2013, respectively; offset by payables to ZionSolutions LLC of $334 million and $414 million as of September 30, 2014 and December 31, 2013, 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.