Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	Mar. 31, 2016 USD ($)
Derivative [Line Items]
Investor-owned utilities, marketers and power producers	$ 781
Energy Cooperatives And Municipalities	909
Financial institutions	116
Other	63
Net Exposure [Member]
Derivative [Line Items]
Investment grade	1,218
Non-investment grade	39
No external ratings - internally rated - investment grade	515
No external ratings - internally rated - non-investment grade	97
Total	1,869
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade	1,276
Non-investment grade	71
No external ratings - internally rated - investment grade	516
No external ratings - internally rated - non-investment grade	101
Total	1,964
Credit Collateral [Member]
Derivative [Line Items]
Investment grade	58
Non-investment grade	32
No external ratings - internally rated - investment grade	1
No external ratings - internally rated - non-investment grade	4
Total	95	[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	436
Non-investment grade	0
No external ratings - internally rated - investment grade	0
No external ratings - internally rated - non-investment grade	0
Total	$ 436

[1] of March 31, 2016, credit collateral held from counterparties where Generation had credit exposure included $8 million of cash and $87 million of letters of credit.Co