Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Dec. 31, 2016 USD ($)
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	$ 995
Non-investment grade	118
Internally rated — investment grade	352
Internally rated — non-investment grade	72
Total	1,537
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	0
Non-investment grade	16
Internally rated — investment grade	1
Internally rated — non-investment grade	8
Total	25
Net Exposure [Member]
Derivative [Line Items]
Investment grade	995
Non-investment grade	102
Internally rated — investment grade	351
Internally rated — non-investment grade	64
Total	1,512
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	328
Non-investment grade	0
Internally rated — investment grade	0
Internally rated — non-investment grade	0
Total	$ 328