Variable Interest Entities - Narrative (Details) $ in Millions		1 Months Ended			3 Months Ended			9 Months Ended
		Jul. 31, 2017 USD ($)	Nov. 30, 2015	Jun. 30, 2015	Sep. 30, 2017 USD ($) VIE	Jun. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) VIE	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) VIE	Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items]
Number Of Variable Interest Entities Consolidated | VIE					6			6		9
Number of Variable Interest Entities not consolidated by equity holders | VIE					7			7		8
Guarantor Obligations, Maximum Exposure, Undiscounted					$ 49			$ 49
Other Nonconsolidated Variable Interest Entity Ownership Interests	[1]				627			627		$ 455
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount					17			17
Payment Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted											$ 245
Financial Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted											165
ExGen Renewables Holdings, LLC [Member]
Variable Interest Entity [Line Items]
Proceeds from Sale of Interest in Partnership Unit		$ 400
ExGen Renewables Holdings, LLC [Member] | Equity interest member [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		49.00%
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value						$ 75
Variable Interest Entity, Financial or Other Support, Amount								$ 31
Related Party Purchase Of Nuclear Output By Third Party Percentage								50.01%
Guarantor Obligations, Liquidation Proceeds, Percentage								49.99%
Other Nonconsolidated Variable Interest Entity Ownership Interests					17			$ 17
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Receivables from affiliates					328			328			$ 400
Exelon Generation Co L L C [Member] | Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests					227			227
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value					8			8
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value					637			637
Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value					$ 275			275
Exelon Generation Co L L C [Member] | Equity interest member [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage					99.00%	90.00%
Exelon Generation Co L L C [Member] | Payment Guarantee [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value						$ 275
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount							$ 27	22	$ 64
2015 ESA Investco, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage				99.00%
2015 ESA Investco, LLC [Member] | Equity interest member [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			69.00%	90.00%
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted					$ 13			13
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount					$ 11		$ 20	$ 39	$ 47

[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.