Retirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended																		8 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Business Services Company [Member]		Mar. 31, 2013 Business Services Company [Member]		Mar. 31, 2014 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member]	Mar. 31, 2014 Commonwealth Edison Co [Member]	Mar. 31, 2013 Commonwealth Edison Co [Member]	Mar. 31, 2014 PECO Energy Co [Member]	Mar. 31, 2013 PECO Energy Co [Member]	Mar. 31, 2014 Baltimore Gas and Electric Company [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member]	Mar. 31, 2014 Pension Plans Defined Benefit [Member]	Mar. 31, 2013 Pension Plans Defined Benefit [Member]	Mar. 31, 2014 Other Postretirement Benefit Plans Defined Benefit [Member]	Mar. 31, 2013 Other Postretirement Benefit Plans Defined Benefit [Member]	Dec. 31, 2014 Other Postretirement Benefit Plans Defined Benefit [Member] Subsequent Event [Member]	Dec. 31, 2014 Other Postretirement Benefit Plans Defined Benefit [Member] NetPeriodicBenefitCostDecrease [Member] Subsequent Event [Member]
Change in benefit obligation:
Service cost															$ 69	$ 80	$ 33	$ 41
Interest cost															183	163	55	48
Plan amendments																				(125)
DefinedBenefitPlanBenefitObligationPeriodIncreaseDecrease																			(800)
Components of net periodic benefit cost:
Service cost															69	80	33	41
Interest cost															183	163	55	48
Amortization of actuarial gain (loss)															105	140	8	20
Prior service cost (credit)															3	3	(4)	(4)
Expected return on assets															(241)	(253)	(38)	(33)
Net periodic benefit cost															119	133	54	72
Changes in plan assets and benefit obligations recognized in OCI and regulatory assets:
Changes in plan assets and benefit obligations recognized in OCI	(13)
Increase in regulatory assets due valuation received by Exelon for its legacy pension and other postretirement benefit obligations.	34
Increase in regulatory liabilities due to updated valuation of Exelon's legacy pension and postretirement benefit obligations	5
Pension And Other Postretirement Benefit Contributions [Abstract]
Pension and non-pension postretirement benefit contributions	472	267					191	115	233	118	11	11	5	5
Defined Benefit Plan Expense Included In Capital And Operational And Maintenance Expense [Abstract]
Amount included in capital and operating & maintenance expense			14	[1]	17	[1]	75	87	56	77	12	11	16	13
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions	29	22	3		2		14	11	7	5	2	2	3	2
Valuation Adjustment Impact [Abstract]
Benefit obligation increase (decrease) reflecting actual census data															$ 35		$ 12

[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.