Variable Interest Entities - Narrative (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2017 USD ($) VIE	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) VIE	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) VIE	Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items]
Number Of Variable Interest Entities Consolidated | VIE		7		7		9
Number of Variable Interest Entities not consolidated by equity holders | VIE		7		7		8
Other Nonconsolidated Variable Interest Entity Ownership Interests	[1]	$ 609,000,000		$ 609,000,000		$ 455,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted		48,000,000		48,000,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		16,000,000		16,000,000
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Other Nonconsolidated Variable Interest Entity Ownership Interests	[1]	577,000,000		577,000,000		423,000,000
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Other Nonconsolidated Variable Interest Entity Ownership Interests	[1]	32,000,000		32,000,000		$ 32,000,000
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Other Nonconsolidated Variable Interest Entity Ownership Interests		16,000,000		16,000,000
Variable Interest Entity, Financial or Other Support, Amount				30,000,000
Guarantor Obligations, Current Carrying Value		75,000,000		$ 75,000,000
Guarantor Obligations, Liquidation Proceeds, Percentage				49.99%
Related Party Purchase Of Nuclear Output By Third Party Percentage				50.01%
Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value		275,000,000		$ 275,000,000
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value		8,000,000		8,000,000
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount		3,000,000	$ 21,000,000	22,000,000	$ 42,000,000
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		13,000,000		13,000,000
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount		8,000,000	$ 12,000,000	27,000,000	$ 26,000,000
Distributed Energy Company [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests		227,000,000		227,000,000
Constellation Energy Nuclear Group [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Receivables from affiliates		324,000,000		324,000,000			$ 400,000,000
Equity Method Investment Variable Interest Entities [Member] | Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value		637,000,000		637,000,000
Payment Guarantee [Member] | Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value		$ 275,000,000		$ 275,000,000
Payment Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted							245,000,000
Financial Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted							$ 165,000,000

[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.