Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Oct. 01, 2015
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent	$ 1,023	$ 1,021
Due to Related Parties, Noncurrent	642	641
Preferred Stock, Value, Issued	0	193
Deferred Finance Costs, Net	204	180
Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	7
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	567	536
Long-term debt (including amounts due within one year)(a)	34,842	25,145
Spent Nuclear Fuel Obligation, Noncurrent	1,023	1,021
Due to Related Parties, Noncurrent	642	641
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	567	536
Long-term debt (including amounts due within one year)(a)	37,626	25,924
Spent Nuclear Fuel Obligation, Noncurrent	856	818
Due to Related Parties, Noncurrent	692	673
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	3
Long-term debt (including amounts due within one year)(a)	1,075	931
Spent Nuclear Fuel Obligation, Noncurrent	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	567	533
Long-term debt (including amounts due within one year)(a)	34,272	23,644
Spent Nuclear Fuel Obligation, Noncurrent	856	818
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)	2,279	1,349
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Due to Related Parties, Noncurrent	692	673
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent	1,023	1,021
Deferred Finance Costs, Net	68	70
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	40	29
Long-term debt (including amounts due within one year)(a)	9,255	8,959
Spent Nuclear Fuel Obligation, Noncurrent	1,023	1,021
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	40	29
Long-term debt (including amounts due within one year)(a)	9,699	9,116
Spent Nuclear Fuel Obligation, Noncurrent	856	818
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
Spent Nuclear Fuel Obligation, Noncurrent	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	40	29
Long-term debt (including amounts due within one year)(a)	8,015	7,767
Spent Nuclear Fuel Obligation, Noncurrent	856	818
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)	1,684	1,349
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Commonwealth Edison Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Due to Related Parties, Noncurrent	205	205
Deferred Finance Costs, Net	47	38
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	10	294
Long-term debt (including amounts due within one year)(a)	7,031	6,509
Due to Related Parties, Noncurrent	205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	10	294
Long-term debt (including amounts due within one year)(a)	8,081	7,069
Due to Related Parties, Noncurrent	218	213
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	10	294
Long-term debt (including amounts due within one year)(a)	8,081	7,069
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	218	213
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Due to Related Parties, Noncurrent	184	184
Deferred Finance Costs, Net	16	15
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)	2,879	2,580
Due to Related Parties, Noncurrent	184	184
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)	3,266	2,786
Due to Related Parties, Noncurrent	207	195
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)	3,266	2,786
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	207	195
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Due to Related Parties, Noncurrent	252	252
Preferred Stock, Value, Issued	0	190	$ 190
Deferred Finance Costs, Net	15	9
Baltimore Gas and Electric Company [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	6
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		213
Long-term debt (including amounts due within one year)(a)	2,662	1,858
Due to Related Parties, Noncurrent	252	252
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		213
Long-term debt (including amounts due within one year)(a)	2,966	2,044
Due to Related Parties, Noncurrent	267	264
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
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		210
Long-term debt (including amounts due within one year)(a)	2,966	2,044
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
Long-term debt (including amounts due within one year)(a)	0	0
Due to Related Parties, Noncurrent	267	264
Pepco Holdings LLC [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		49
Pepco Holdings LLC [Member] | Reported Value Measurement [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	517
Long-term debt (including amounts due within one year)(a)	6,044
Pepco Holdings LLC [Member] | Reported Value Measurement [Member] | Predecessor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		958
Long-term debt (including amounts due within one year)(a)		5,279
Preferred Stock, Value, Issued		183
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	517
Long-term debt (including amounts due within one year)(a)	6,292
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
Long-term debt (including amounts due within one year)(a)		5,817
Preferred Stock, Value, Issued		183
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	517
Long-term debt (including amounts due within one year)(a)	5,698
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
Long-term debt (including amounts due within one year)(a)		5,231
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)	594
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
Preferred Stock, Value, Issued		183
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	30	31
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		64
Long-term debt (including amounts due within one year)(a)	2,350	2,351
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
Long-term debt (including amounts due within one year)(a)	3,002	2,673
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
Long-term debt (including amounts due within one year)(a)	3,000	2,673
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)	2	0
Delmarva Power and Light Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	10	10
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	17	105
Long-term debt (including amounts due within one year)(a)	1,265	1,265
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	17	105
Long-term debt (including amounts due within one year)(a)	1,378	1,288
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	17	105
Long-term debt (including amounts due within one year)(a)	1,277	1,185
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)	101	103
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net	6	6
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		5
Long-term debt (including amounts due within one year)(a)	1,167	1,201
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
Long-term debt (including amounts due within one year)(a)	1,357	1,324
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
Long-term debt (including amounts due within one year)(a)	1,058	1,044
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)	$ 299	$ 280