Retirement Benefits - Narrative (Details) - USD ($) $ in Millions					3 Months Ended			12 Months Ended
		Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2014	Jun. 30, 2016	Mar. 31, 2016	Mar. 23, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Increase (Decrease) in Pension Plan Obligations						$ 35
Benefit obligation increase (decrease) reflecting actual census data						8
AOCI valuation adjustment						2
Regulatory asset increase (decrease) due to updated valuation adjustment						27
Defined benefit plan, amounts recognized In regulatory liabilities, before tax						$ 3
Expected qualified pension plan contributions		$ 310						$ 310
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		23						23
Expected other postretirement benefit plan contributions		$ 44						$ 44
Projected Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded Percentage		80.00%						80.00%		81.00%
Accumulated Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded Percentage		84.00%						84.00%		85.00%
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		$ 127						$ 127
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		6						6
Expected other postretirement benefit plan contributions		12						12
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		33						33
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		1						1
Expected other postretirement benefit plan contributions		2						2
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		23						23
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		1						1
Expected other postretirement benefit plan contributions		0						0
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		38						38
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		2						2
Expected other postretirement benefit plan contributions		16						16
Pepco Holdings LLC [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		60						60
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		8						8
Expected other postretirement benefit plan contributions		12						12
Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Increase (decrease) in pension obligation					$ 25
Pepco Holdings LLC [Member] | Projected Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded Percentage										81.00%
Pepco Holdings LLC [Member] | Accumulated Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded Percentage										89.00%
Potomac Electric Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		60						60
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		1						1
Expected other postretirement benefit plan contributions		10						10
Delmarva Power and Light Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		0						0
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		0						0
Expected other postretirement benefit plan contributions		0						0
Atlantic City Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		0						0
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		0						0
Expected other postretirement benefit plan contributions		0						0
Constellation Legacy Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions		$ 21						$ 21
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.04%		3.94%				4.04%		4.29%		3.94%
Current year actuarial loss (gain)								$ 644		$ 476		$ 1,639
Regulatory asset increase (decrease) due to updated valuation adjustment								$ 959		$ (46)		$ 415
Expected return on plan assets		7.00%						7.00%	[1]	7.00%	[1]	7.00%	[1]
Discount rate								4.29%	[2]	3.94%	[3]	4.80%	[4]
Increase (decrease) in pension obligation				$ 361
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		$ 1,360						$ 1,360
Amortization of actuarial loss								(554)		$ (571)		$ (420)
Current year prior service (credit) cost								(60)		0		0
Amortization of prior service (cost) credit								(14)		(13)		(14)
Settlements								0		(2)		(2)
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[5]							$ 1,010		(110)		$ 1,203
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate				4.20%								4.20%
Current year actuarial loss (gain)							$ 0			50		$ 276
Regulatory asset increase (decrease) due to updated valuation adjustment							$ (13)			$ (6)		$ 212
Expected return on plan assets	[1]						6.50%			6.50%		7.00%
Discount rate	[2]									4.20%		5.05%
Amortization of actuarial loss							$ (14)			$ (65)		$ (45)
Amortization of prior service (cost) credit							0			(2)		(2)
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[5]						$ (14)			$ (17)		$ 229
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	[1]						5.00%			5.00%		5.00%
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets								6.50%
Discount rate								3.96%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.04%		3.92%				4.04%		4.29%		3.92%
Current year actuarial loss (gain)								$ (101)		$ (194)		$ 561
Regulatory asset increase (decrease) due to updated valuation adjustment								$ 95		$ (60)		$ (217)
Expected return on plan assets		6.60%	6.71%					6.71%	[1]	6.50%	[1]	6.59%	[1]
Discount rate								4.29%	[2]	3.92%	[3]	4.90%	[4]
Increase (decrease) in pension obligation				$ 117
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		$ 244						$ 244
Amortization of actuarial loss								(63)		$ (80)		$ (50)
Current year prior service (credit) cost								0		(23)		(1,012)
Amortization of prior service (cost) credit								185		174		122
Settlements								0		0		0
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[5]							$ 115		$ (123)		$ (379)
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate				4.15%						4.55%		4.15%
Current year actuarial loss (gain)							$ 0			$ (39)		$ 62
Regulatory asset increase (decrease) due to updated valuation adjustment							$ 1			$ (34)		$ 72
Expected return on plan assets	[1]						6.75%			6.75%		7.25%
Discount rate	[2]						4.55%			4.15%		5.00%
Amortization of actuarial loss							$ (2)			$ (8)		$ (3)
Amortization of prior service (cost) credit							3			13		13
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[5]						$ 1			$ (34)		$ 72
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	[1]						5.00%			5.00%		5.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets								6.75%
Discount rate								3.80%

[1] Not applicable to pension and other postretirement benefit plans that do not have plan asset

[2] )The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2016. Certain benefit plans used individual rates ranging from 3.68%-4.14% and 4.32%-4.43% for pension and other postretirement plans, respectivel

[3] The discount rates above represent the blended rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2015. Certain benefit plans used individual rates ranging from 3.29%-3.82% and 3.99%-4.06% for pension and other postretirement plans, respectively.

[4] The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2014. Certain of the other postretirement benefit plans were remeasured as of April 30, 2014 using an expected long-term rate of return on plan assets of 6.59% and a discount rate of 4.30%. Costs for the year ended December 31, 2014 reflect the impact of this remeasurement. On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became the sponsor of CENG’s legacy pension and OPEB plans effective July 14, 2014; discount rates for those plans, impacting 2014 costs, ranged from 3.60%-4.30% and 4.09%-4.55%, respectively. See Note 5 - Investment in Constellation Energy Nuclear Group, LLC for further information.

[5] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjY2ZTAyZGU0MjJhODQwMGQ4YTI0ZmVhYjg5OGIyNGRifFRleHRTZWxlY3Rpb246QjAwMzBCMDJERTBGRUQzOTAyOTc5RjkyNUQyMzhDMUEM}