Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Jun. 30, 2016 USD ($)
Derivative [Line Items]
Investor-owned utilities, marketers and power producers	$ 573
Energy Cooperatives And Municipalities	696
Financial institutions	96
Other	30
Net Exposure [Member]
Derivative [Line Items]
Investment grade	953
Non-investment grade	31
No external ratings - internally rated - investment grade	372
No external ratings - internally rated - non-investment grade	39
Total	1,395
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	965
Non-investment grade	55
No external ratings - internally rated - investment grade	373
No external ratings - internally rated - non-investment grade	46
Total	1,439
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	12
Non-investment grade	24
No external ratings - internally rated - investment grade	1
No external ratings - internally rated - non-investment grade	7
Total	44	[1]
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade	1
Non-investment grade	0
No external ratings - internally rated - investment grade	0
No external ratings - 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	356
Non-investment grade	0
No external ratings - internally rated - investment grade	0
No external ratings - internally rated - non-investment grade	0
Total	$ 356

[1] of June 30, 2016, credit collateral held from counterparties where Generation had credit exposure included $9 million of cash and $35 million of letters of credit.