Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Variable Interest Entity [Line Items]
Total assets	$ 597	[1]	$ 460	[1]
Total liabilities	286	[1]	140	[1]
Our ownership interest	9	[1]	86	[1]
Other ownership interests	302	[1]	234	[1]
Pledged assets for Zion Station decommissioning	319		458
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Pledged assets for Zion Station decommissioning	319		458
Payable To Thirdparty To Decommission Nuclear Plant Funded By Pledged Assets	292	[2]	414	[2]
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	506	[1]	128	[1]
Total liabilities	237	[1]	17	[1]
Our ownership interest	0	[1]	0	[1]
Other ownership interests	269	[1]	111	[1]
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	91	[1]	332	[1]
Total liabilities	49	[1]	123	[1]
Our ownership interest	9	[1]	86	[1]
Other ownership interests	33	[1]	123	[1]
Investments [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	13		74
Investments [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	0		7
Investments [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	13		67
Contract Intangible Asset [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	9		9
Contract Intangible Asset [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	9		9
Contract Intangible Asset [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	0		0
Payment Guarantee [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	3		5
Payment Guarantee [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	0		0
Payment Guarantee [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	3		5
Asset Held In Trust Noncurrent [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	27	[3]	44	[3]
Asset Held In Trust Noncurrent [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	27	[3]	44	[3]
Asset Held In Trust Noncurrent [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Our maximum exposure to loss	$ 0	[3]	$ 0	[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] 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.

[3] 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 $319 million and $458 million as of December 31, 2014 and December 31, 2013, respectively; offset by payables to ZionSolutions LLC of $292 million and $414 million as of December 31, 2014 and December 31, 2013, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE.