Debt and Credit Agreements - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended	3 Months Ended	5 Months Ended	9 Months Ended
	Jun. 30, 2014	Sep. 30, 2017	May 26, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2014	Mar. 23, 2017	Jan. 09, 2017	Jun. 30, 2016	Mar. 31, 2016	Jan. 13, 2016	Aug. 10, 2013	Jan. 31, 2013	Aug. 01, 2011
Debt Instrument [Line Items]
Derivative, Notional Amount									$ 100,000,000	$ 600,000,000
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value		$ 1,150,000,000		$ 1,150,000,000
Extinguishment of Debt, Amount					$ 11,000,000
Repayments of Long-term Debt				1,728,000,000	944,000,000
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Junior Subordinated Notes		$ 1,150,000,000		$ 1,150,000,000
Equity Units Issued	23
Debt Instrument, Convertible, Conversion Price	$ 50
Interest Rate	2.50%	3.497%		3.497%
Loss on Reissuance, Treasury Stock				$ 1,050,000,000
Stock Issued During Period, Shares, Treasury Stock Reissued				33
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity												$ 500,000,000
Line of Credit Facility, Increase (Decrease), Net			$ 600,000,000
Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable							$ 500,000,000
Debt Instrument, Interest Rate Terms				LIBOR plus 1%
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable											$ 500,000,000
Debt Instrument, Interest Rate Terms				LIBOR plus 1%
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity														$ 1,500,000,000
Line of Credit Facility, Increase (Decrease), Net			$ 900,000,000
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 541,000,000	164,000,000
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity								$ 100,000,000					$ 75,000,000
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 41,000,000	$ 39,000,000
Preferred Stock, Par or Stated Value Per Share		$ 25.19		$ 25.19
Preferred Stock, Dividend Rate, Percentage		6.20%
ExGen Texas Power [Member] | Exelon Generation Co L L C [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 675,000,000
Derivative, Notional Amount						$ 505,000,000
Derivative, Fixed Interest Rate		2.34%		2.34%
Long-term Debt, Gross		$ 660,000,000		$ 660,000,000
Line of Credit Facility, Maximum Borrowing Capacity		20,000,000		20,000,000
EGTP475Sep2021 [Member] | Exelon Generation Co L L C [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 6,000,000		6,000,000
Debt Instrument, Interest Rate Terms		LIBOR + 4.75%				LIBOR plus 4.75%
AGEPFNotesNov2017 [Member] | Exelon Generation Co L L C [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 14,000,000		$ 14,000,000
Debt Instrument, Interest Rate Terms		LIBOR + 1.25%
AGEPFNotesNov2017 [Member] | AGE Biomass project [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms				LIBOR + 1.25%
Interest Expense, Long-term Debt				$ 6,000,000
Repayments of Long-term Debt				$ 228,000,000