Investment in Constellation Energy Nuclear Group, LLC - Narrative (Details) - USD ($) $ in Millions			3 Months Ended								9 Months Ended	12 Months Ended
		Apr. 01, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 09, 2015
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure			$ 50									$ 50
Income (Loss) from Equity Method Investments												(24)	$ (7)	$ 0
Revenues			7,875	$ 9,002	$ 6,910	$ 7,573	$ 6,702	$ 7,401	$ 6,514	$ 8,830		31,360	29,447	27,429
Accumulated other comprehensive loss, net			(2,660)				(2,624)					(2,660)	(2,624)
Operating revenues from affiliates												10	9	23
Parental guarantee provided			75									75
Business Combination, Integration Related Costs	[1],[2]											143	87
Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated other comprehensive loss, net		$ 1,500
Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure		245
Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure		165
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Cash distribution paid to member												922	2,474	645
Income (Loss) from Equity Method Investments										19		0	0	(20)
Revenues			4,388	$ 5,035	$ 3,589	$ 4,739	4,294	$ 4,768	$ 4,232	5,840		17,751	19,135	17,393
Accumulated other comprehensive loss, net			(54)				(63)					(54)	(63)
AOCI Tax, Attributable to Parent										77
Allocation of federal tax benefit under tax sharing agreement			94				$ 57				$ 55	94	57	55
Operating revenues from affiliates												1,439	749	779
Parental guarantee provided			21									21
Business Combination, Integration Related Costs	[2]											37	24
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Remeasurement gain from derecognition of equity method investment		261
Business combination, step acquisition, equity interest in acquiree, fair value		136
Business acquisition, preexisting relationship, gain (loss) recognized		132
Parental guarantee provided		7	7									7			$ 275
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Revenues										17		548	509
Investment in CENG										1,900
Accumulated other comprehensive loss, net										$ 116
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Due from Affiliates		$ 400	$ 316									$ 316
Debt Instrument, Interest Rate, Stated Percentage		5.25%
Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased		85.00%										50.00%
Other Intangible Assets, Net		$ 152
Reduction to net income attributable to noncontrolling interest												$ 20	18
Net Income (Loss) Attributable to Parent												201	(11)
Business Combination, Integration Related Costs												2
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Due to affiliate		$ 205
Exelon Generation Co L L C [Member] | EDFI [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Operating revenues from affiliates												$ 376	$ 488	$ 137
Electricite De France LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest			49.99%									49.99%
Electricite De France LLC [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased		15.00%										50.00%
Electricite De France LLC [Member] | Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee obligations maximum exposure		$ 145
Constellation Energy Group LLC [Member]
Schedule of Equity Method Investments [Line Items]
Investment Interest Rate											8.50%
Constellation Energy Group LLC [Member] | EDFI [Member]
Schedule of Equity Method Investments [Line Items]
Cash distribution paid to member		$ 400

[1] Reflects costs (benefits) recorded at Exelon related to financing, including mark-to-market activity on forward-starting interest rate swaps.

[2] The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above.