Variable Interest Entities Variable Intereste Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,134	$ 1,205
Total liabilities	[1]	265	502
Exelon's ownership interest in VIE	[1]	251	248
Other ownership interests in VIE	[1]	618	455
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		251	264
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		8	9
Debt and payment guarantees
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	3
Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	[2]	2	9
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	625	638
Total liabilities	[1]	37	215
Exelon's ownership interest in VIE	[1]	0	0
Other ownership interests in VIE	[1]	588	423
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	9
Commercial Agreement Variable Interest Entities [Member] | Debt and payment guarantees
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	0
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	9
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	509	567
Total liabilities	[1]	228	287
Exelon's ownership interest in VIE	[1]	251	248
Other ownership interests in VIE	[1]	30	32
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		251	264
Equity Investment VIE [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	0
Equity Investment VIE [Member] | Debt and payment guarantees
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	3
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]
Registrants maximum exposure to loss		8
Held-to-maturity Securities Pledged as Collateral		39	113
Accounts Payable, Interest-bearing, Noncurrent	[3]	$ 37	$ 104

[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 $39 million and $113 million as of December 31, 2017 and December 31, 2016, respectively; offset by payables to ZionSolutions LLC of $37 million and $104 million as of December 31, 2017 and December 31, 2016, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE

[3] Included in Other current assets within Exelon’s and Generation’s Consolidated Balance Sheets in 2017