Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent	$ 1,022,000,000	$ 1,021,000,000
Long-term Debt and Capital Lease Obligations, Current	2,058,000,000	1,500,000,000
Due to Related Parties, Noncurrent	641,000,000	641,000,000
Preferred Stock, Value, Issued	193,000,000	193,000,000
Deferred Finance Costs, Net	179,000,000	180,000,000
Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	7,000,000
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	3,643,000,000	536,000,000
Long-term debt (including amounts due within one year)(a)	31,372,000,000	25,145,000,000
SNF obligation	1,022,000,000	1,021,000,000
Due to Related Parties, Noncurrent	641,000,000	641,000,000
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	3,643,000,000	536,000,000
Long-term debt (including amounts due within one year)(a)	32,844,000,000	25,924,000,000
SNF obligation	817,000,000	818,000,000
Due to Related Parties, Noncurrent	670,000,000	673,000,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	3,000,000	3,000,000
Long-term debt (including amounts due within one year)(a)	1,132,000,000	931,000,000
SNF obligation	0	0
Due to Related Parties, Noncurrent	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	3,640,000,000	533,000,000
Long-term debt (including amounts due within one year)(a)	29,577,000,000	23,644,000,000
SNF obligation	817,000,000	818,000,000
Due to Related Parties, Noncurrent	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	2,135,000,000	1,349,000,000
SNF obligation	0	0
Due to Related Parties, Noncurrent	670,000,000	673,000,000
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent	1,022,000,000	1,021,000,000
Long-term Debt and Capital Lease Obligations, Current	177,000,000	90,000,000
Deferred Finance Costs, Net	72,000,000	70,000,000
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	1,529,000,000	29,000,000
Long-term debt (including amounts due within one year)(a)	9,052,000,000	8,959,000,000
SNF obligation	1,022,000,000	1,021,000,000
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	1,529,000,000	29,000,000
Long-term debt (including amounts due within one year)(a)	9,088,000,000	9,116,000,000
SNF obligation	817,000,000	818,000,000
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	0	0
SNF obligation	0	0
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	1,529,000,000	29,000,000
Long-term debt (including amounts due within one year)(a)	7,539,000,000	7,767,000,000
SNF obligation	817,000,000	818,000,000
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	1,549,000,000	1,349,000,000
SNF obligation	0	0
Commonwealth Edison Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current	665,000,000	665,000,000
Due to Related Parties, Noncurrent	205,000,000	205,000,000
Deferred Finance Costs, Net	37,000,000	38,000,000
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	1,000,000
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	643,000,000	294,000,000
Long-term debt (including amounts due within one year)(a)	6,510,000,000	6,509,000,000
Due to Related Parties, Noncurrent	205,000,000	205,000,000
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	643,000,000	294,000,000
Long-term debt (including amounts due within one year)(a)	7,357,000,000	7,069,000,000
Due to Related Parties, Noncurrent	207,000,000	213,000,000
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	0	0
Due to Related Parties, Noncurrent	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	643,000,000	294,000,000
Long-term debt (including amounts due within one year)(a)	7,357,000,000	7,069,000,000
Due to Related Parties, Noncurrent	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	0	0
Due to Related Parties, Noncurrent	207,000,000	213,000,000
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current	300,000,000	300,000,000
Due to Related Parties, Noncurrent	184,000,000	184,000,000
Deferred Finance Costs, Net	14,000,000	15,000,000
PECO Energy Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)(a)	2,581,000,000	2,580,000,000
Due to Related Parties, Noncurrent	184,000,000	184,000,000
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)(a)	2,900,000,000	2,786,000,000
Due to Related Parties, Noncurrent	196,000,000	195,000,000
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)(a)	0	0
Due to Related Parties, Noncurrent	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)(a)	2,900,000,000	2,786,000,000
Due to Related Parties, Noncurrent	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)(a)	0	0
Due to Related Parties, Noncurrent	196,000,000	195,000,000
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current	378,000,000	378,000,000
Due to Related Parties, Noncurrent	252,000,000	252,000,000
Preferred Stock, Value, Issued	190,000,000	190,000,000
Deferred Finance Costs, Net	9,000,000	9,000,000
Baltimore Gas and Electric Company [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	6,000,000
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	153,000,000	213,000,000
Long-term debt (including amounts due within one year)(a)	1,859,000,000	1,858,000,000
Due to Related Parties, Noncurrent	252,000,000	252,000,000
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	153,000,000	213,000,000
Long-term debt (including amounts due within one year)(a)	2,119,000,000	2,044,000,000
Due to Related Parties, Noncurrent	267,000,000	264,000,000
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	3,000,000	3,000,000
Long-term debt (including amounts due within one year)(a)	0	0
Due to Related Parties, Noncurrent	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	150,000,000	210,000,000
Long-term debt (including amounts due within one year)(a)	2,119,000,000	2,044,000,000
Due to Related Parties, Noncurrent	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	0	0
Due to Related Parties, Noncurrent	267,000,000	264,000,000
Pepco Holdings, LLC [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Preferred Stock, Value, Issued		183,000,000
Pepco Holdings, LLC [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current	476,000,000
Preferred Stock, Value, Issued	0
Pepco Holdings, LLC [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current		456,000,000
Deferred Finance Costs, Net		49,000,000
Pepco Holdings, LLC [Member] | Reported Value Measurement [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	1,317,000,000
Long-term Debt and Capital Lease Obligations, Current	6,132,000,000
Pepco Holdings, LLC [Member] | Reported Value Measurement [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		958,000,000
Long-term Debt and Capital Lease Obligations, Current		5,279,000,000
Preferred Stock, Value, Issued		183,000,000
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	1,317,000,000
Long-term debt (including amounts due within one year)(a)	6,126,000,000
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		958,000,000
Long-term debt (including amounts due within one year)(a)		5,817,000,000
Preferred Stock, Value, Issued		183,000,000
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0
Long-term debt (including amounts due within one year)(a)	0
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)		0
Preferred Stock, Value, Issued		0
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	1,317,000,000
Long-term debt (including amounts due within one year)(a)	5,540,000,000
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		958,000,000
Long-term debt (including amounts due within one year)(a)		5,231,000,000
Preferred Stock, Value, Issued		0
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0
Long-term debt (including amounts due within one year)(a)	586,000,000
Pepco Holdings, LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)		586,000,000
Preferred Stock, Value, Issued		183,000,000
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current	11,000,000	11,000,000
Deferred Finance Costs, Net	31,000,000	31,000,000
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		64,000,000
Long-term Debt and Capital Lease Obligations, Current	2,352,000,000	2,351,000,000
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		64,000,000
Long-term debt (including amounts due within one year)(a)	2,876,000,000	2,673,000,000
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	0	0
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		64,000,000
Long-term debt (including amounts due within one year)(a)	2,876,000,000	2,673,000,000
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	0	0
Delmarva Power and Light Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current	218,000,000	204,000,000
Deferred Finance Costs, Net	10,000,000	10,000,000
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	75,000,000	105,000,000
Long-term Debt and Capital Lease Obligations, Current	1,265,000,000	1,265,000,000
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	75,000,000	105,000,000
Long-term debt (including amounts due within one year)(a)	1,341,000,000	1,288,000,000
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	0	0
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	75,000,000	105,000,000
Long-term debt (including amounts due within one year)(a)	1,238,000,000	1,185,000,000
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	0	0
Long-term debt (including amounts due within one year)(a)	103,000,000	103,000,000
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt and Capital Lease Obligations, Current	47,000,000	48,000,000
Deferred Finance Costs, Net	6,000,000	6,000,000
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		5,000,000
Long-term Debt and Capital Lease Obligations, Current	1,191,000,000	1,201,000,000
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		5,000,000
Long-term debt (including amounts due within one year)(a)	1,369,000,000	1,324,000,000
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	0	0
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		5,000,000
Long-term debt (including amounts due within one year)(a)	1,081,000,000	1,044,000,000
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	$ 288,000,000	$ 280,000,000