Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,127	$ 1,134
Total liabilities	[1]	262	265
Exelon's ownership interest in VIE	[1]	246	251
Other ownership interests in VIE	[1]	618	618
Registrants' maximum exposure to loss		9
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		246	251
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		8	8
Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	[2]	2	2
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	626	625
Total liabilities	[1]	37	37
Exelon's ownership interest in VIE	[1]	0	0
Other ownership interests in VIE	[1]	588	588
Commercial Agreement Variable Interest Entities [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		0	0
Commercial Agreement Variable Interest Entities [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		8	8
Commercial Agreement Variable Interest Entities [Member] | Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	[2]	2	2
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	501	509
Total liabilities	[1]	225	228
Exelon's ownership interest in VIE	[1]	246	251
Other ownership interests in VIE	[1]	30	30
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		246	251
Equity Investment VIE [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		0	0
Equity Investment VIE [Member] | Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	[2]	0	0
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Other ownership interests in VIE		9
Held-to-maturity Securities Pledged as Collateral	[3]	30	39
Accounts Payable, Interest-bearing, Noncurrent	[4],[5]	$ 28	$ 37

[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 $30 million and $39 million as of March 31, 2018 and December 31, 2017, respectively; offset by payables to ZionSolutions, LLC of $28 million and $37 million as of March 31, 2018 and December 31, 2017, respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE. See Note 13 — Nuclear Decommissioning for additional details.

[3] Included in Other current assets within Exelon's and Generation's Consolidated Balance sheets.

[4] 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.

[5] Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.