Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Dec. 31, 2015 USD ($)
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	$ 1,397
Non-investment grade	67
Internally rated—investment grade	521
Internally rated—non-investment grade	77
Total	2,062
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	50
Non-investment grade	25
Internally rated—investment grade	0
Internally rated—non-investment grade	7
Total	82
Net Exposure [Member]
Derivative [Line Items]
Investment grade	1,347
Non-investment grade	42
Internally rated—investment grade	521
Internally rated—non-investment grade	70
Total	1,980
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	1
Non-investment grade	0
Internally rated—investment grade	0
Internally rated—non-investment grade	0
Total	1
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	432
Non-investment grade	0
Internally rated—investment grade	0
Internally rated—non-investment grade	0
Total	$ 432