Retirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended					6 Months Ended
	Jun. 30, 2014		Mar. 31, 2014	Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Changes in plan assets and benefit obligations recognized in OCI and regulatory assets:
Changes in plan assets and benefit obligations recognized in OCI	$ 1		$ (12)
Increase in regulatory assets due valuation received by Exelon for its legacy pension and other postretirement benefit obligations.	15		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						499		284
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions	19			21		48		43
CENGMember [Member]
Defined Benefit Plan Expense Included In Capital And Operational And Maintenance Expense [Abstract]
Amount included in capital and operating & maintenance expense						5
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions						1
Business Services Company [Member]
Defined Benefit Plan Expense Included In Capital And Operational And Maintenance Expense [Abstract]
Amount included in capital and operating & maintenance expense	13	[1]		16	[1]	26	[1]	34	[1]
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions	1			2		4		4
Business Services Company [Member] | Remeasurement [Member]
Design Changes Impact [Abstract]
Other comprehensive income (loss) due to design changes	(259)
Exelon Generation Co L L C [Member]
Pension And Other Postretirement Benefit Contributions [Abstract]
Pension and non-pension postretirement benefit contributions						210		120
Defined Benefit Plan Expense Included In Capital And Operational And Maintenance Expense [Abstract]
Amount included in capital and operating & maintenance expense	63			87		139		173
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions	10			10		24		21
Exelon Generation Co L L C [Member] | CENGMember [Member]
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions						1
Commonwealth Edison Co [Member]
Pension And Other Postretirement Benefit Contributions [Abstract]
Pension and non-pension postretirement benefit contributions						236		119
Defined Benefit Plan Expense Included In Capital And Operational And Maintenance Expense [Abstract]
Amount included in capital and operating & maintenance expense	40			77		96		154
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions	5			5		12		10
PECO Energy Co [Member]
Pension And Other Postretirement Benefit Contributions [Abstract]
Pension and non-pension postretirement benefit contributions						11		10
Defined Benefit Plan Expense Included In Capital And Operational And Maintenance Expense [Abstract]
Amount included in capital and operating & maintenance expense	9			10		21		21
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions	2			2		4		4
Baltimore Gas and Electric Company [Member]
Pension And Other Postretirement Benefit Contributions [Abstract]
Pension and non-pension postretirement benefit contributions						8		11
Defined Benefit Plan Expense Included In Capital And Operational And Maintenance Expense [Abstract]
Amount included in capital and operating & maintenance expense	17			14		33		27
Defined Contribution Plan Contributions By Employer [Abstract]
Savings plan matching contributions	1			2		4		4
Pension Plans Defined Benefit [Member]
Change in benefit obligation:
Service cost	69	[2]		79		138	[2]	159
Interest cost	184	[2]		163		367	[2]	326
Settlements				0				0
Change in plan assets:
Settlements				0				0
Components of net periodic benefit cost:
Service cost	69	[2]		79		138	[2]	159
Interest cost	184	[2]		163		367	[2]	326
Settlement charges	0	[2]				0	[2]
Amortization of actuarial gain (loss)	104	[2]		141		209	[2]	281
Prior service cost (credit)	4	[2]		4		7	[2]	7
Expected return on assets	(242)	[2]		(254)		(483)	[2]	(508)
Contractual termination benefit cost								0
Net periodic benefit cost	119	[2]		133		238	[2]	265
Valuation Adjustment Impact [Abstract]
Benefit obligation increase (decrease) reflecting actual census data	13		35
Pension Plans Defined Benefit [Member] | Exelon Generation Co L L C [Member] | CENGMember [Member]
Change in benefit obligation:
Service cost	5					5
Interest cost	6					6
Components of net periodic benefit cost:
Service cost	5					5
Interest cost	6					6
Expected return on assets	(9)					9
Net periodic benefit cost	2					2
Other Postretirement Benefit Plans Defined Benefit [Member]
Change in benefit obligation:
Service cost	29	[2]		40		61	[2]	81
Interest cost	45	[2]		49		101	[2]	97
Components of net periodic benefit cost:
Service cost	29	[2]		40		61	[2]	81
Interest cost	45	[2]		49		101	[2]	97
Amortization of actuarial gain (loss)	12	[2]		21		20	[2]	42
Prior service cost (credit)	(30)	[2]		(6)		(34)	[2]	(10)
Expected return on assets	(38)	[2]		(33)		(76)	[2]	(66)
Curtailments charges				0				0
Contractual termination benefit cost								0
Net periodic benefit cost	18	[2]		71		72	[2]	144
Changes in plan assets and benefit obligations recognized in OCI and regulatory assets:
Amortization of transition obligation				0				0
Valuation Adjustment Impact [Abstract]
Benefit obligation increase (decrease) reflecting actual census data	3		12
Other Postretirement Benefit Plans Defined Benefit [Member] | Subsequent Event [Member]
Change in benefit obligation:
DefinedBenefitPlanBenefitObligationPeriodIncreaseDecrease	(790)
Other Postretirement Benefit Plans Defined Benefit [Member] | NetPeriodicBenefitCostDecrease [Member] | Subsequent Event [Member]
Change in benefit obligation:
Plan amendments	(149)
Other Postretirement Benefit Plans Defined Benefit [Member] | Business Services Company [Member] | Remeasurement [Member]
Valuation Adjustment Impact [Abstract]
Regulatory asset increase (decrease) due to updated valuation adjustment	125
Design Changes Impact [Abstract]
Regulatory Asset increase (decrease) due to design changes	(240)
Other Postretirement Benefit Plans Defined Benefit [Member] | Exelon Generation Co L L C [Member] | CENGMember [Member]
Change in benefit obligation:
Service cost	1					1
Interest cost	2					2
Components of net periodic benefit cost:
Service cost	1					1
Interest cost	2					2
Net periodic benefit cost	$ 3					$ 3

[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] Excludes components of CENG’s net periodic benefit costs for the period April 1, 2014 to June 30, 2014 as presented in the below table.