Variable Interest Entities Variable Intereste Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,069	$ 1,134
Total liabilities	[1]	259	265
Exelon's ownership interest in VIE	[1]	223	251
Other ownership interests in VIE	[1]	587	618
Registrants maximum exposure to loss		15
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		223	251
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		7	8
Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	[2]	0	2
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets		597	625
Total liabilities		37	37
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		560	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		7	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		0	2
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets		472	509
Total liabilities		222	228
Exelon's ownership interest in VIE		223	251
Other ownership interests in VIE		27	30
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		223	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		0	0
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		13
Nuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Held-to-maturity Securities Pledged as Collateral	[3]	9	39
Accounts Payable, Interest-bearing, Noncurrent		$ 9	$ 37

[1] These items represent amounts on the unconsolidated VIE balance sheets, not in 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 in 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 $9 million and $39 million as of December 31, 2018 and December 31, 2017, respectively; offset by payables to ZionSolutions LLC of $9 million and $37 million as of December 31, 2018 and December 31, 2017, respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE.

[3] (a)Included in Other current liabilities within Exelon's and Generation's Consolidated Balance Sheets. Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized gains and losses associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized.