Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Sep. 30, 2016 USD ($)
Derivative [Line Items]
Investor-owned utilities, marketers and power producers	$ 757
Energy Cooperatives And Municipalities	712
Financial institutions	117
Other	58
Net Exposure [Member]
Derivative [Line Items]
Investment grade	1,013
Non-investment grade	153
No external ratings - internally rated - investment grade	420
No external ratings - internally rated - non-investment grade	58
Total	1,644
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	1,017
Non-investment grade	175
No external ratings - internally rated - investment grade	423
No external ratings - internally rated - non-investment grade	61
Total	1,676
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	4
Non-investment grade	22
No external ratings - internally rated - investment grade	3
No external ratings - internally rated - non-investment grade	3
Total	32	[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	355
Non-investment grade	0
No external ratings - internally rated - investment grade	0
No external ratings - internally rated - non-investment grade	0
Total	$ 355

[1] of September 30, 2016, credit collateral held from counterparties where Generation had credit exposure included $10 million of cash and $22 million of letters of credit. The credit collateral does not include non-liquid collateral.