Mergers, Acquisitions, and Dispositions - Narrative (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended								0 Months Ended		9 Months Ended			0 Months Ended			3 Months Ended	9 Months Ended				0 Months Ended
	Sep. 30, 2014		Sep. 30, 2014		Sep. 30, 2013	Aug. 18, 2014	Jun. 30, 2014	Jun. 11, 2014	May 01, 2014	Dec. 31, 2013	Aug. 08, 2014 Pepco Holdings [Member]	Jul. 18, 2014 Pepco Holdings [Member]	Sep. 30, 2014 Pepco Holdings [Member]	Jul. 18, 2014 Pepco Holdings [Member]	Jun. 11, 2014 Pepco Holdings [Member]	Jul. 18, 2014 Pepco Holdings [Member] Minimum [Member]	Jul. 18, 2014 Pepco Holdings [Member] Maximum [Member]	Jul. 29, 2014 Exelon Generation Co L L C [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member]	Mar. 31, 2014 Exelon Generation Co L L C [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member]	Jun. 11, 2014 Junior Subordinated Debt [Member] Pepco Holdings [Member]	Jun. 11, 2014 Bridge Loan [Member] Pepco Holdings [Member]	Sep. 30, 2014 Electricity Generation Plant, Non-Nuclear [Member]
Payments to Acquire Businesses and Interest in Affiliates [Abstract]
Payments to Acquire Businesses, Gross			$ 67,000,000		$ 0													$ 60,000,000		$ 67,000,000	$ 0
Business Combination, Integration Related Costs													57,000,000
Other Payments to Acquire Businesses																			260,000,000
Business Combination Proposed Customer Benefits Package														100,000,000
Business Exit Costs																259,000,000	293,000,000
Cash Funding From Non Core Asset Sale															1,000,000,000
Expected Debt Issuance													3,500,000,000
Subordinated Debt, Amount															1,200,000,000
Equity Security units			57.5																					23.0
Line of Credit Facility, Maximum Borrowing Capacity	8,500,000,000	[1]	8,500,000,000	[1]																					7,200,000,000
Bridge Loan							3,900,000,000	3,900,000,000	7,200,000,000
Equity Method Investment, Ownership Percentage						67.00%																50.01%
Gain on Sale of Investments											329,000,000
Equity Method Investment, Net Sales Proceeds											615,000,000
Cash offered in exchange for each share of PHI stock														$ 27.25	$ 35
Payments to Acquire Assets, Investing Activities												90,000,000
Other Long-term Investments														18,000,000
Other Long Term Investments Maximum														180,000,000
Other noncurrent assets	1,139,000,000		1,139,000,000							964,000,000			108,000,000						714,000,000	714,000,000			645,000,000
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds													7,200,000,000
Expected Pre-Tax proceeds	1,300,000,000
Assets Held-for-sale, at Carrying Value																										$ 900,000,000

[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 expired on October 17, 2014 and were renewed at the same amount through October 16, 2015. These facilities are solely utilized to issue letters of credit. As of September 30, 2014, letters of credit issued under these agreements for Generation, ComEd, PECO and BGE totaled $9 million, $18 million, $21 million and $1 million, respectively. Also, excludes the unsecured bridge credit facility of $3.9 billion to support the PHI transaction discussed below, as well as, applicable asset divestitures.