Debt and Credit Agreements - Retirement and Redemptions of Current and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Apr. 06, 2015	Apr. 15, 2015
Debt Instrument [Line Items]
Repayments of Long-term Debt	$ 580	$ 1,150
Senior Notes [Member] | SeniorSecuredNotes455Jun152015 [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt	550
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Interest Rate	3.71%
Repayments of Long-term Debt	18	532
Exelon Generation Co L L C [Member] | AVSR [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt	4
Exelon Generation Co L L C [Member] | Clear Horizon solar [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt	2
Exelon Generation Co L L C [Member] | Continental Wind 6000 February 28, 2033 [Member]
Debt Instrument [Line Items]
Interest Rate		6.00%
Repayments of Long-term Debt	10	11
Exelon Generation Co L L C [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt	2
Exelon Generation Co L L C [Member] | Senior Notes [Member] | SeniorSecuredNotes525January152014Member [Member]
Debt Instrument [Line Items]
Interest Rate		5.35%
Repayments of Long-term Debt		500
Exelon Generation Co L L C [Member] | Senior Notes [Member] | AVSR [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt			2
Exelon Generation Co L L C [Member] | Senior Notes [Member] | SeniorSecuredNotes455Jun152015 [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt	550
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Interest Rate		4.10%
Repayments of Long-term Debt		20
Exelon Generation Co L L C [Member] | Capital Lease Obligations [Member] | Continental Wind 6000 February 28, 2033 [Member]
Debt Instrument [Line Items]
Interest Rate		7.83%
Repayments of Long-term Debt	1	1
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds, April 1, 2017 [Member] | Rate Stabilization Bonds, April 1, 2017 [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt			37
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt	0	617
Commonwealth Edison Co [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Interest Rate		5.85%
Repayments of Long-term Debt		17
Commonwealth Edison Co [Member] | First Mortgage Bonds [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				260
Commonwealth Edison Co [Member] | First Mortgage Bonds [Member] | FirstMortgageBond163January12014 [Member]
Debt Instrument [Line Items]
Interest Rate		1.63%
Repayments of Long-term Debt		$ 600