Retirement Benefits - Pension and Other Postretirement Benefit Plan Target Asset Allocations (Details)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets		100.00%	100.00%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets		100.00%	100.00%
Equity Securities [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		43.00%
Percentage of Plan Assets		47.00%	43.00%
Equity Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		33.00%
Percentage of Plan Assets		33.00%	35.00%
Fixed Income Securities [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		28.00%
Percentage of Plan Assets		29.00%	27.00%
Fixed Income Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		39.00%
Percentage of Plan Assets		39.00%	34.00%
Alternative Investments [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	[1]	29.00%
Percentage of Plan Assets	[1]	24.00%	30.00%
Alternative Investments [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	[1]	28.00%
Percentage of Plan Assets	[1]	28.00%	31.00%
Predecessor [Member] | Pepco Holdings LLC [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets			100.00%
Predecessor [Member] | Pepco Holdings LLC [Member] | Equity Securities [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets			63.00%
Predecessor [Member] | Pepco Holdings LLC [Member] | Equity Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets			28.00%
Predecessor [Member] | Pepco Holdings LLC [Member] | Fixed Income Securities [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets			34.00%
Predecessor [Member] | Pepco Holdings LLC [Member] | Fixed Income Securities [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets			66.00%
Predecessor [Member] | Pepco Holdings LLC [Member] | Alternative Investments [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets	[1]		3.00%
Predecessor [Member] | Pepco Holdings LLC [Member] | Alternative Investments [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets	[1]		6.00%

[1] ___(a)Alternative investments include private equity, hedge funds, real estate, and private