Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2017
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	100.00%
Minimum expectation of tax position to be realized	50.00%
Restatement Adjustment [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Impact of Prior Period Adjustment on Opening Retained Earnings, Net of Tax				$ 11
Impact of Prior Period Adjustment on Opening Regulatory Assets				18
Impact of Prior Period Adjustment on Deferred Income Taxes and Unamortized Investment Tax Credits				7
Prior Period Adjustment of Operating Revenues		$ 7	$ 7
Impact of Prior Period Adjustment on Prior Year Income, Net of Tax		$ 5	$ 7
Impact of Prior Period Adjustment on Earnings Per Share, Basic		$ 0.01	$ 0.01
Impact of Prior Period Adjustment on Earnings Per Share, Diluted		$ (0.00)	$ 0.01
Restatement Adjustment [Member] | Pepco Holdings LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Impact of Prior Period Adjustment on Opening Retained Earnings, Net of Tax				11
Impact of Prior Period Adjustment on Opening Regulatory Assets				18
Impact of Prior Period Adjustment on Deferred Income Taxes and Unamortized Investment Tax Credits				7
Prior Period Adjustment of Operating Revenues		$ 7	$ 7
Impact of Prior Period Adjustment on Prior Year Income, Net of Tax		5	7
Restatement Adjustment [Member] | Potomac Electric Power Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Impact of Prior Period Adjustment on Opening Retained Earnings, Net of Tax				11
Impact of Prior Period Adjustment on Opening Regulatory Assets				18
Impact of Prior Period Adjustment on Deferred Income Taxes and Unamortized Investment Tax Credits				$ 7
Prior Period Adjustment of Operating Revenues		7	7
Impact of Prior Period Adjustment on Prior Year Income, Net of Tax		$ 5	$ 7
Commonwealth Edison Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	99.00%
CENG [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.01%
ExGen Renewables [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	51.00%
Minimum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	20.00%
Maximum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.00%