Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Cash Collateral Posted		$ 19
Letters Of Credit Posted		10
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Financial institutions		89
Investor-owned utilities, marketers and power producers		563
Energy Cooperatives And Municipalities		560
Other		134
Cash Collateral Posted		517	$ 347
Letters Of Credit Posted		278	$ 284
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade		878
Non-investment grade		47
No external ratings - internally rated - investment grade		327
No external ratings - internally rated - non-investment grade		123
Total		1,375
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Derivative [Line Items]
Investment grade		14
Non-investment grade		1
No external ratings - internally rated - investment grade		0
No external ratings - internally rated - non-investment grade		14
Total	[1]	29
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Investment grade		864
Non-investment grade		46
No external ratings - internally rated - investment grade		327
No external ratings - internally rated - non-investment grade		109
Total		1,346
Exelon Generation Co L L C [Member] | 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
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade		299
Non-investment grade		0
No external ratings - internally rated - investment grade		0
No external ratings - internally rated - non-investment grade		0
Total		$ 299

[1] As of June 30, 2017, credit collateral held from counterparties where Generation had credit exposure included $19 million of cash and $10 million of letters of credit. The credit collateral does not include non-liquid collateral.