Retirement Benefits - Contributions made to Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended	12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense					$ 621		$ 637		$ 561
Pension and non-pension postretirement benefit contributions					397		502		617
Expected qualified pension plan contributions				$ 310	310
Service cost					164		148		103
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				44	44
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				23	23
Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense	[1]				48		57		46
Service cost	[2]				19		11		10
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions							462		332
Service cost					250
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				1,360	1,360
Pension Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					39	[3]	47		26
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					50		40	[4]	291	[4]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				244	244
Other Postretirement Benefit Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					3		3	[4]	20	[4]
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense					218		269		250
Pension and non-pension postretirement benefit contributions					152		245		297
Expected qualified pension plan contributions				127	127
Service cost					79		80		51
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				12	12
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				6	6
Exelon Generation Co L L C [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					140	[3]	231		173
Exelon Generation Co L L C [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					12		14	[4]	124	[4]
Exelon Corporate [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					6	[3]	5		9
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense					166		206		162
Pension and non-pension postretirement benefit contributions					38		150		248
Expected qualified pension plan contributions				33	33
Service cost					34		32		26
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				2	2
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				1	1
Commonwealth Edison Co [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					33	[3]	143		122
Commonwealth Edison Co [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					5		7	[4]	125	[4]
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense					33		39		36
Pension and non-pension postretirement benefit contributions					30		40		16
Expected qualified pension plan contributions				23	23
Service cost					10		11		8
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				0	0
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				1	1
PECO Energy Co [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					30	[3]	40		11
PECO Energy Co [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					0		0	[4]	5	[4]
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense					68		66		67
Pension and non-pension postretirement benefit contributions					49		17		16
Expected qualified pension plan contributions				38	38
Service cost	[5]				12		14		8
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				16	16
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				2	2
Baltimore Gas and Electric Company [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					31	[3]	1		0
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					18		16	[4]	17	[4]
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected qualified pension plan contributions				60	60
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				12	12
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				8	8
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense		$ 9			47		37		16
Service cost		1			6		6		6
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense		23					97		58
Pension and non-pension postretirement benefit contributions		4					21		18
Service cost		3					14		13
Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense				88
Pension and non-pension postretirement benefit contributions				86
Service cost				10
Pepco Holdings LLC [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost					60
Pepco Holdings LLC [Member] | Pension Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		4	[3]		17	[3]	0		0
Pepco Holdings LLC [Member] | Pension Plan, Defined Benefit [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[3]	4					0		0
Pepco Holdings LLC [Member] | Pension Plan, Defined Benefit [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[3]			74
Pepco Holdings LLC [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					2		0	[4]	0	[4]
Pepco Holdings LLC [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[3]	0					5		4
Pepco Holdings LLC [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[3]			12
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense		7			31		30		22
Pension and non-pension postretirement benefit contributions					32		14		11
Expected qualified pension plan contributions				60	60
Service cost		1			3		3		3
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				10	10
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				1	1
Potomac Electric Power Company [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					24	[3]	0		0
Potomac Electric Power Company [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					8		2	[4]	1	[4]
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense		4			18		15		7
Pension and non-pension postretirement benefit contributions					22		0		0
Expected qualified pension plan contributions				0	0
Service cost		1			2		2		2
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				0	0
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				0	0
Delmarva Power and Light Company [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					22	[3]	0		0
Delmarva Power and Light Company [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					0		0	[4]	0	[4]
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension And Other Postretirement Benefit Expense Included In Capital And Operating And Maintenance Expense		$ 3			15		15		13
Pension and non-pension postretirement benefit contributions					17		2		3
Expected qualified pension plan contributions				0	0
Service cost					2		2		1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year				0	0
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				0	0
Atlantic City Electric Company [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					15	[3]	0		0
Atlantic City Electric Company [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					2		3	[4]	$ 3	[4]
Constellation Legacy Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[3]				36		$ 43
Expected qualified pension plan contributions				$ 21	$ 21
Remeasurement [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes							6.59%
Remeasurement [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes							4.30%
Remeasurement [Member] | Maximum [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes					4.43%		4.06%		4.55%

[1] ___(a)These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO, BGE, Pepco, DPL or ACE amounts

[2] (b)These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These costs are not included in the Generation, ComEd, PECO, or BGE amount

[3] Includes $6 million, $5 million, and $9 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2016, 2015, and 2014, respectively.

[4] _________________________(a)Exelon's and Generation's pension contributions include $25 million, $36 million and $43 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the years ended December 31, 2016, 2015 and 2014, respectively.

[5] ____(a)Includes $13 million, $9 million and $5 million related to CENG for the years ended December 31, 2016, December 31, 2015 and for the period from April 1, 2014 to December 31, 2014, respe