Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 4,789	$ 4,570
Regulatory liabilities	602	369
Noncurrent regulatory liabilities	4,187	4,201
Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	47	94
Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,607	2,577
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,601	1,527
Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	185	92
Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8	9
Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	76	95
Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	20	28
Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	134	131
Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1
Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	72	16
Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	39
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	644	639
Regulatory liabilities	127	112
Noncurrent regulatory liabilities	517	527
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	438	405
PECO Energy Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	41	40
PECO Energy Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8	9
PECO Energy Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	76	95
PECO Energy Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	20	28
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	56	60
PECO Energy Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PECO Energy Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5	2
PECO Energy Co [Member] | Over Recovered NonBypassable Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	10
PECO Energy Co [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	160	222
Regulatory liabilities	50	38
Noncurrent regulatory liabilities	110	184
Baltimore Gas and Electric Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		14
Baltimore Gas and Electric Company [Member] | Over-Recovered Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		5
Baltimore Gas and Electric Company [Member] | Abandonment costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	141	195
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	18
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1
Baltimore Gas and Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	19	8
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Gas Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Electric Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		30
Baltimore Gas and Electric Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		213
Regulatory liabilities		66
Noncurrent regulatory liabilities		147
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	237
Regulatory liabilities	79
Noncurrent regulatory liabilities	158
Pepco Holdings LLC [Member] | Other Postretirement Benefits [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Pepco Holdings LLC [Member] | Other Postretirement Benefits [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Asset Retirement Obligations [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Pepco Holdings LLC [Member] | Asset Retirement Obligations [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Removal Costs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		150
Pepco Holdings LLC [Member] | Removal Costs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	136
Pepco Holdings LLC [Member] | Energy Efficiency Demand Response Programs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1
Pepco Holdings LLC [Member] | Energy Efficiency Demand Response Programs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3
Pepco Holdings LLC [Member] | Dlc Program Cost [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Pepco Holdings LLC [Member] | Dlc Program Cost [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Electric Transmission And Distribution Tax Repairs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Pepco Holdings LLC [Member] | Electric Transmission And Distribution Tax Repairs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Gas Distribution Tax Repairs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Pepco Holdings LLC [Member] | Gas Distribution Tax Repairs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Over Recovered Energy And Transmission Costs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		27
Pepco Holdings LLC [Member] | Over Recovered Energy And Transmission Costs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	18
Pepco Holdings LLC [Member] | Over Recovered Decoupling Revenue [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Pepco Holdings LLC [Member] | Regulatory Liabilities Other [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		35
Pepco Holdings LLC [Member] | Regulatory Liabilities Other [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	41
Pepco Holdings LLC [Member] | Deferred Lease Revenue [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	39
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	31	44
Regulatory liabilities	11	15
Noncurrent regulatory liabilities	20	29
Potomac Electric Power Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	5	14
Potomac Electric Power Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	18	21
Potomac Electric Power Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3	0
Potomac Electric Power Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8	16
Potomac Electric Power Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Potomac Electric Power Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2	7
Potomac Electric Power Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	140	160
Regulatory liabilities	43	49
Noncurrent regulatory liabilities	97	111
Delmarva Power and Light Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3	11
Delmarva Power and Light Company [Member] | Over-Recovered Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities		4
Delmarva Power and Light Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	118	129
Delmarva Power and Light Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5	19
Delmarva Power and Light Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Delmarva Power and Light Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	17	12
Delmarva Power and Light Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	25	25
Regulatory liabilities	25	18
Noncurrent regulatory liabilities	0	7
Atlantic City Electric Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	4
Atlantic City Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	1
Atlantic City Electric Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5	8
Atlantic City Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Atlantic City Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	20	16
Atlantic City Electric Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3,698	3,614
Regulatory liabilities	329	155
Noncurrent regulatory liabilities	3,369	3,459
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Asset Retirement Obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,169	2,172
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,324	1,332
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	141	52
Commonwealth Edison Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	60	53
Commonwealth Edison Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Commonwealth Edison Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4	5
Commonwealth Edison Co [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Commonwealth Edison Co [Member] | Renewable energy Requirements [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 30	$ 24