Retirement Benefits - Narrative (Details) (USD $)	3 Months Ended			1 Months Ended	3 Months Ended					9 Months Ended				3 Months Ended					9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	9 Months Ended	6 Months Ended			3 Months Ended		9 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	5 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Apr. 30, 2014 Remeasurement [Member]	Jun. 30, 2014 Exelon Legacy Benefit Plans [Member]	Sep. 30, 2014 Business Services Company [Member]		Sep. 30, 2013 Business Services Company [Member]		Sep. 30, 2014 Business Services Company [Member]		Sep. 30, 2013 Business Services Company [Member]		Sep. 30, 2014 Business Services Company [Member] Remeasurement [Member]	Sep. 30, 2014 Exelon Generation Co L L C [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2014 Exelon Generation Co L L C [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member]		Sep. 30, 2014 Exelon Generation Co L L C [Member] CENG [Member]	Sep. 30, 2014 Commonwealth Edison Co [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2014 Commonwealth Edison Co [Member]	Sep. 30, 2013 Commonwealth Edison Co [Member]	Sep. 30, 2014 PECO Energy Co [Member]	Sep. 30, 2013 PECO Energy Co [Member]	Sep. 30, 2014 PECO Energy Co [Member]	Sep. 30, 2013 PECO Energy Co [Member]	Sep. 30, 2014 Baltimore Gas and Electric Company [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Baltimore Gas and Electric Company [Member]	Sep. 30, 2013 Baltimore Gas and Electric Company [Member]	Sep. 30, 2014 Constellation Energy Nuclear Group [Member]	Mar. 31, 2014 Pension Plan, Defined Benefit [Member]	Sep. 30, 2014 Pension Plan, Defined Benefit [Member]	Sep. 30, 2014 Pension Plan, Defined Benefit [Member] CENG [Member]	Sep. 30, 2014 Pension Plan, Defined Benefit [Member] CENG [Member]	Jun. 30, 2014 Pension Plan, Defined Benefit [Member] Exelon Legacy Benefit Plans [Member]	Sep. 30, 2014 Pension Plan, Defined Benefit [Member] Exelon Legacy Benefit Plans [Member]	Sep. 30, 2014 Pension Plan, Defined Benefit [Member] CENG [Member]	Sep. 30, 2014 Pension Plan, Defined Benefit [Member] CENG [Member] Minimum [Member]	Sep. 30, 2014 Pension Plan, Defined Benefit [Member] CENG [Member] Maximum [Member]	Sep. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member]	Mar. 31, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member]	Sep. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member]	Sep. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member] CENG [Member]	Sep. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member] CENG [Member]	Jun. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member] Exelon Legacy Benefit Plans [Member]	Aug. 31, 2014 Other Postretirement Benefit Plan, Defined Benefit [Member] CENG [Member]	Sep. 30, 2014 Exelon Sponsored Benefit Plan [Member]	Sep. 30, 2014 Exelon Sponsored Benefit Plan [Member] Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation increase (decrease) reflecting actual census data																																					$ 35,000,000										$ 12,000,000
Changes in plan assets and benefit obligations recognized in OCI		1,000,000	12,000,000
Increase in regulatory assets due valuation received by Exelon for its legacy pension and other postretirement benefit obligations.			34,000,000
Increase in regulatory liabilities due to updated valuation of Exelon's legacy pension and postretirement benefit obligations			5,000,000
Pension Obligations Valuation Adjustment																																									13,000,000
Other postretirement benefit obligation increase (decrease) due to updated valuation adjustment	790,000,000																																																		3,000,000
Regulatory asset increase (decrease) due to updated valuation adjustment					15,000,000									125,000,000
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense				149,000,000		11,000,000	[1]	24,000,000	[1]	37,000,000	[1]	58,000,000	[1]		54,000,000	[2]	87,000,000	[2]	193,000,000	[2]	259,000,000	[2]		33,000,000	77,000,000	129,000,000	231,000,000	7,000,000	11,000,000	28,000,000	32,000,000	17,000,000	14,000,000	50,000,000	41,000,000				2,000,000	5,000,000									3,000,000	6,000,000
Regulatory Asset increase (decrease) due to design changes	240,000,000
Other comprehensive income (loss) due to design changes																																														259,000,000
Expected return on assets																																						7.00%					7.75%			6.59%
Discount rate																																										4.80%		3.60%	4.30%	4.30%		4.90%				4.55%
Expected qualified pension plan contributions	308,000,000														160,000,000				160,000,000					119,000,000		119,000,000		11,000,000		11,000,000		0		0		43,000,000																	53,000,000	51,000,000
Expected non-qualified pension plan contributions	18,000,000														9,000,000				9,000,000				3,000,000	1,000,000		1,000,000		0		0		1,000,000		1,000,000
Expected other postretirement benefit plan contributions	$ 290,000,000														$ 128,000,000				$ 128,000,000				$ 5,000,000	$ 121,000,000		$ 121,000,000		$ 4,000,000		$ 4,000,000		$ 18,000,000		$ 18,000,000

[1] These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO or BGE amounts above.

[2] For the three months ended September 30, 2014, the cost for pension benefits and other postretirement benefits related to CENG were $2 million and $3 million, respectively. For the period April 1, 2014 to September 30, 2014, the cost for pension benefits and other postretirement benefits related to CENG were $5 million and $6 million, respectively. CENG is not included in the 2013 amounts.