Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Property Plant And Equipment [Line Items]
Less: accumulated depreciation	$ (12,579)	[1]	$ (12,184)	[2]
Property, plant and equipment, net	45,784		45,186
Property Plant And Equipment Footnotes [Abstract]
Accumulated amortization of nuclear fuel	2,221		2,078
Exelon Generation Co L L C [Member]
Property Plant And Equipment [Line Items]
Less: accumulated depreciation	(6,347)	[1]	(6,014)	[2]
Property, plant and equipment, net	19,813		19,531
Property Plant And Equipment Footnotes [Abstract]
Accumulated amortization of nuclear fuel	2,221		2,078
Commonwealth Edison Co [Member]
Property Plant And Equipment [Line Items]
Less: accumulated depreciation	(2,969)		(2,998)
Property, plant and equipment, net	14,020		13,826
PECO Energy Co [Member]
Property Plant And Equipment [Line Items]
Less: accumulated depreciation	(2,840)		(2,797)
Property, plant and equipment, net	6,141		6,078
Baltimore Gas and Electric Company [Member]
Property Plant And Equipment [Line Items]
Less: accumulated depreciation	(2,627)		(2,595)
Property, plant and equipment, net	$ 5,568		$ 5,498

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $2,221 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $2,078 million.