Mergers, Acquisitions, and Dispositions - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 23, 2016	Mar. 31, 2015	Dec. 31, 2015	Jul. 31, 2014
Business Acquisition [Line Items]
Revenues	$ 7,573,000,000		$ 8,830,000,000
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross	6,645,000,000		15,000,000
Business Combination, Integration Related Costs	102,000,000		108,000,000
Investments	$ 455,000,000			$ 639,000,000
Cash offered in exchange for each share of PHI stock	$ 27.25
Other noncurrent assets	$ 1,398,000,000			1,445,000,000
Other Commitment	6,282,000,000
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent	59,000,000
Business Combination, Contingent Consideration, Asset	235,000,000
Net income	123,000,000		738,000,000
Common Stock [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross		$ 180,000,000
Other Investments [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment	130,000,000
Pepco Holdings, LLC [Member]
Business Acquisition [Line Items]
Revenues	107,000,000
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment	508,000,000
Net income	(315,000,000)
Pepco Holdings, LLC [Member] | Common Stock [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross	6,933,000,000
Pepco Holdings, LLC [Member] | Common Stock [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross	180,000,000
PEPCO Holdings Inc [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross	7,142,000,000
Other Commitment	444,000,000
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Revenues	4,739,000,000		5,840,000,000
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross	1,000,000		15,000,000
Business Combination, Integration Related Costs	16,000,000		7,000,000
Investments	$ 250,000,000			210,000,000
Equity Method Investment, Ownership Percentage	50.01%
Other noncurrent assets	$ 650,000,000			627,000,000
Total liabilities held for sale (b)	5,000,000
Gain (Loss) on Disposition of Property Plant Equipment	32,000,000
Other Commitment	5,468,000,000				$ 91,000,000
Net income	257,000,000		485,000,000
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Revenues	291,000,000		334,000,000
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	13,000,000		1,000,000
Other noncurrent assets	22,000,000			19,000,000
Total assets held for sale	1,000,000
Other Commitment	8,000,000
Net income	(100,000,000)		9,000,000
Atlantic City Electric Company [Member] | Pepco Holdings, LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment	120,000,000
Equity Contribution	49,000,000
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Revenues	551,000,000		545,000,000
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Investments	99,000,000			68,000,000
Other noncurrent assets	5,000,000			4,000,000
Total assets held for sale	4,000,000
Gain (Loss) on Disposition of Property Plant Equipment	8,000,000
Other Commitment	15,000,000
Net income	(108,000,000)		26,000,000
Potomac Electric Power Company [Member] | Pepco Holdings, LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment	139,000,000
Equity Contribution	73,000,000
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Revenues	362,000,000		421,000,000
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Combination, Integration Related Costs	16,000,000		1,000,000
Other noncurrent assets	8,000,000			$ 2,000,000
Other Commitment	12,000,000
Net income	(72,000,000)		$ 32,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings, LLC [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Other Commitment	104,000,000
Equity Contribution	$ 46,000,000