Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Mar. 31, 2017 USD ($)
Derivative [Line Items]
Investor-owned utilities, marketers and power producers	$ 600
Energy Cooperatives And Municipalities	663
Financial institutions	101
Other	93
Net Exposure [Member]
Derivative [Line Items]
Investment grade	948
Non-investment grade	72
No external ratings - internally rated - investment grade	324
No external ratings - internally rated - non-investment grade	113
Total	1,457
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	964
Non-investment grade	75
No external ratings - internally rated - investment grade	324
No external ratings - internally rated - non-investment grade	127
Total	1,490
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	16
Non-investment grade	3
No external ratings - internally rated - investment grade	0
No external ratings - internally rated - non-investment grade	14
Total	33	[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	313
Non-investment grade	0
No external ratings - internally rated - investment grade	0
No external ratings - internally rated - non-investment grade	0
Total	$ 313

[1] of March 31, 2017, credit collateral held from counterparties where Generation had credit exposure included $23 million of cash and $10 million of letters of credit. The credit collateral does not include non-liquid collateral.