Significant Accounting Policies - Summary of Total Interest Incurred, Capitalized and Credits to AFUDC (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2],[3]	$ 1,170	$ 1,144	$ 1,423
Capitalized interest	[1],[3]	79	63	54
Credits to AFUDC debt and equity	[1],[3]	44	37	35
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2],[3]	445	419	411
Capitalized interest	[1],[3]	79	63	54
Credits to AFUDC debt and equity	[1],[3]	0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[2]	336	323	584
Capitalized interest		0	0	0
Credits to AFUDC debt and equity		9	5	16
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[2]	116	115	117
Capitalized interest		0	0	0
Credits to AFUDC debt and equity		7	8	6
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2]	113	118	129
Capitalized interest	[1]	0	0	0
Credits to AFUDC debt and equity	[1]	$ 28	$ 24	$ 13

[1] .

[2] Includes interest expense to affiliates.

[3] On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, the 2014 financial results include CENG’s financial position and results of operations beginning April 1, 2014.