Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 512,000,000	$ 369,000,000
Noncurrent	4,378,000,000	4,201,000,000
Regulatory Liabilities	4,890,000,000	4,570,000,000
Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	89,000,000	95,000,000
Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	93,000,000	94,000,000
Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,599,000,000	2,577,000,000
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,669,000,000	1,527,000,000
Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	42,000,000
Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	122,000,000	92,000,000
Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9,000,000	9,000,000
Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	25,000,000	28,000,000
Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	187,000,000	131,000,000
Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,000,000
Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	55,000,000	16,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	61,000,000	38,000,000
Noncurrent	151,000,000	184,000,000
Regulatory Liabilities	212,000,000	222,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,000,000	14,000,000
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] | Abandonment costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,000,000	1,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Gas Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5,000,000	1,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Electric Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	31,000,000
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	187,000,000	195,000,000
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] | 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	15,000,000	18,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,000,000
Baltimore Gas and Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	10,000,000	8,000,000
Baltimore Gas and Electric Company [Member] | Over-Recovered Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	14,000,000	5,000,000
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	134,000,000	112,000,000
Noncurrent	521,000,000	527,000,000
Regulatory Liabilities	655,000,000	639,000,000
PECO Energy Co [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4,000,000	3,000,000
PECO Energy Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	89,000,000	95,000,000
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	417,000,000	405,000,000
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	43,000,000	40,000,000
PECO Energy Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9,000,000	9,000,000
PECO Energy Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	25,000,000	28,000,000
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Over Recovered Electric Transmission Costs	3,000,000
Regulatory Liabilities	69,000,000	60,000,000
Default Service Provider Program Costs	36,000,000	35,000,000
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	3,000,000	2,000,000
PECO Energy Co [Member] | Over-Recovered Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	26,000,000	22,000,000
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	150,000,000	155,000,000
Noncurrent	3,489,000,000	3,459,000,000
Regulatory Liabilities	3,639,000,000	3,614,000,000
Commonwealth Edison Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,182,000,000	2,172,000,000
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,334,000,000	1,332,000,000
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	78,000,000	52,000,000
Commonwealth Edison Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		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	43,000,000	53,000,000
Over Recovered electric Supply Costs	17,000,000	29,000,000
Renewable Energy Requirement Revenue	26,000,000	24,000,000
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	2,000,000	5,000,000
PEPCO Holdings Inc [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		66,000,000
Noncurrent		147,000,000
Regulatory Liabilities		213,000,000
PEPCO Holdings Inc [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	106,000,000
Noncurrent	186,000,000
Regulatory Liabilities	292,000,000
PEPCO Holdings Inc [Member] | Electric Transmission And Distribution Tax Repairs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PEPCO Holdings Inc [Member] | Electric Transmission And Distribution Tax Repairs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PEPCO Holdings Inc [Member] | Abandonment costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4,000,000
PEPCO Holdings Inc [Member] | Other Postretirement Benefits [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PEPCO Holdings Inc [Member] | Other Postretirement Benefits [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PEPCO Holdings Inc [Member] | Nuclear Decommissioning [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PEPCO Holdings Inc [Member] | Nuclear Decommissioning [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PEPCO Holdings Inc [Member] | Removal Costs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		150,000,000
PEPCO Holdings Inc [Member] | Removal Costs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	148,000,000
PEPCO Holdings Inc [Member] | Deferred Lease Revenue [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	42,000,000
PEPCO Holdings Inc [Member] | Energy Efficiency Demand Response Programs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,000,000
PEPCO Holdings Inc [Member] | Energy Efficiency Demand Response Programs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,000,000
PEPCO Holdings Inc [Member] | Dlc Program Cost [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PEPCO Holdings Inc [Member] | Dlc Program Cost [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PEPCO Holdings Inc [Member] | Gas Distribution Tax Repairs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PEPCO Holdings Inc [Member] | Gas Distribution Tax Repairs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PEPCO Holdings Inc [Member] | Over Recovered Energy And Transmission Costs [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		27,000,000
PEPCO Holdings Inc [Member] | Over Recovered Energy And Transmission Costs [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	60,000,000
PEPCO Holdings Inc [Member] | Over Recovered Decoupling Revenue [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PEPCO Holdings Inc [Member] | Regulatory Liabilities Other [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		35,000,000
PEPCO Holdings Inc [Member] | Regulatory Liabilities Other [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	41,000,000
PEPCO Holdings Inc [Member] | Deferred Income Tax Charge [Member] | Predecessor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	26,000,000	15,000,000
Noncurrent	29,000,000	29,000,000
Regulatory Liabilities	55,000,000	44,000,000
Potomac Electric Power Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	15,000,000	14,000,000
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] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	21,000,000	21,000,000
Potomac Electric Power Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Dlc Program Cost [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	25,000,000	16,000,000
Over Recovered electric Supply Costs	10,000,000	2,000,000
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	9,000,000	7,000,000
Potomac Electric Power Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Delmarva Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	57,000,000	49,000,000
Noncurrent	109,000,000	111,000,000
Regulatory Liabilities	166,000,000	160,000,000
Delmarva Power and Light Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	12,000,000	11,000,000
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] | Abandonment costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3,000,000
Delmarva Power and Light Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	127,000,000	129,000,000
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] | 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	25,000,000	19,000,000
Over Recovered electric Supply Costs	7,000,000	4,000,000
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	14,000,000	12,000,000
Delmarva Power and Light Company [Member] | Over-Recovered Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6,000,000	4,000,000
Delmarva Power and Light Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	22,000,000	18,000,000
Noncurrent	5,000,000	7,000,000
Regulatory Liabilities	27,000,000	25,000,000
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] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Nuclear Decommissioning [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	1,000,000	1,000,000
Atlantic City Electric Company [Member] | Dlc Program Cost [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	10,000,000	8,000,000
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	$ 16,000,000	16,000,000
Atlantic City Electric Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 0