Variable Interest Entities - Narrative (Details)		3 Months Ended
		Mar. 31, 2017 USD ($) VIE	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) VIE	Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items]
Other Commitment		$ 3,212,000,000
Variable Interest Entity, Financial or Other Support, Amount		$ 27,000,000
Number of Variable Interest Entities not consolidated by equity holders | VIE		7		8
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		$ 16,000,000
Number Of Variable Interest Entities Consolidated | VIE		9		9
Guarantor Obligations, Current Carrying Value		$ 75,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted		48,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value		275,000,000
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Measure of Activity, Other, Amount		0.5001
Other Commitment		2,404,000,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		$ 16,000,000
Related Party Purchase Of Nuclear Output By Third Party Percentage		49.99%
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
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
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Other Commitment		266,000,000
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount		19,000,000	$ 20,000,000
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Other Commitment		8,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted		13,000,000
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount		19,000,000	$ 14,000,000
Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests		227,000,000
Constellation Energy Nuclear Group [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Receivables from affiliates		320,000,000			$ 400,000,000
Financial Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted					165,000,000
Payment Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Payables to affiliates					$ 245,000,000
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
Investments [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		279,000,000		$ 264,000,000
Investments [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		0		0
Investments [Member] | Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		279,000,000		264,000,000
Finite-Lived Intangible Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		9,000,000		9,000,000
Finite-Lived Intangible Assets [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		9,000,000		9,000,000
Finite-Lived Intangible Assets [Member] | Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		0		0
Debt [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		0		3,000,000
Debt [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		0		0
Debt [Member] | Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		0		3,000,000
Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	[1]	7,000,000		9,000,000
Other Assets [Member] | Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	[1]	7,000,000		9,000,000
Other Assets [Member] | Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	[1]	$ 0		$ 0

[1] 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 $95 million and $113 million as of March 31, 2017 and December 31, 2016, respectively; offset by payables to ZionSolutions LLC of $88 million and $104 million as of March 31, 2017 and December 31, 2016, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE.