Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,064	$ 1,069
Total liabilities	[1]	265	259
Exelon's ownership interest in VIE	[1]	214	223
Other ownership interests in VIE	[1]	585	587
Registrants' maximum exposure to loss		16
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		214	223
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		7	7
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets		601	597
Total liabilities		42	37
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		559	560
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	7
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets		463	472
Total liabilities		223	222
Exelon's ownership interest in VIE		214	223
Other ownership interests in VIE		26	27
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		214	223
Equity Investment VIE [Member] | Contract intangible asset
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		$ 12

[1] These items represent amounts in 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.