Mergers, Acquisitions, and Dispositions - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions			3 Months Ended	6 Months Ended		12 Months Ended
		Jan. 21, 2015	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Jul. 18, 2014	Jun. 11, 2014	May. 01, 2014	Mar. 31, 2014
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross				$ 28.0	$ 66.0
Business Combination, Integration Related Costs				$ 89.0
Temporary Equity, Share Subscriptions			57.5	57.5				57.5
Line of Credit Facility, Maximum Borrowing Capacity	[1]		$ 8,500.0	$ 8,500.0
Bridge Loan									$ 7,200.0
Other noncurrent assets			1,388.0	1,388.0		$ 1,160.0
Business Acquisition, Preacquisition Contingency, Amount of Settlement			300.0	300.0
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized				205.0
Proceeds from Issuance of Common Stock			1,870.0
Pepco Holdings [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Acquisition, Transaction Costs								$ 116.0
Temporary Equity, Share Subscriptions								23.0
Line of Credit Facility, Maximum Borrowing Capacity								$ 7,200.0
Cash offered in exchange for each share of PHI stock						$ 35	$ 27.25
Other Long-term Investments							$ 18.0
Other noncurrent assets			162.0	162.0
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds				7,200.0
Business Acquisition, Preacquisition Contingency, Amount of Settlement			66.0	66.0
Pepco Holdings [Member] | Workforce Development [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Customer Loyalty Program Liability, Noncurrent			14.4	14.4
Pepco Holdings [Member] | Energy Efficiency Program [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Customer Loyalty Program Liability, Noncurrent			43.2	43.2
Pepco Holdings [Member] | Minimum [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Exit Costs						$ 259.0
Pepco Holdings [Member] | Maximum [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Exit Costs						293.0
Other Long-term Investments							$ 180.0
Delmarva Power & Light [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Business Acquisition, Preacquisition Contingency, Amount of Settlement			40.0	40.0
Delmarva Power & Light [Member] | Workforce Development [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Customer Loyalty Program Liability, Noncurrent			2.0	2.0
Delmarva Power & Light [Member] | Energy Efficiency Program [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Customer Loyalty Program Liability, Noncurrent			2.0	2.0
Exelon Generation Co L L C [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross				28.0	66.0
Equity Method Investment, Ownership Percentage										50.01%
Other noncurrent assets			$ 798.0	$ 798.0		731.0
Debt Instrument, Face Amount					$ 3,200.0
Proceeds from Sale of Productive Assets		$ 1,800.0
Junior Subordinated Debt [Member] | Pepco Holdings [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Subordinated Debt, Amount						$ 1,200.0

[1] Excludes additional credit facility agreements for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. These facilities expire on October 16, 2015. These facilities are solely utilized to issue letters of credit. As of June 30, 2015, letters of credit issued under these agreements for Generation, ComEd, PECO and BGE totaled $7 million, $16 million, $21 million and $1 million, respectively.