Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent		$ 1,136	$ 1,024
Due to Related Parties, Noncurrent		641	641
Deferred Finance Costs, Net		199	200
Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		7	7
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		2,048	1,267
Long-term debt (including amounts due within one year)(a)	[1]	34,689	34,005
Spent Nuclear Fuel Obligation, Noncurrent		1,136	1,024
Due to Related Parties, Noncurrent	[2]	641	641
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		2,048	1,267
Long-term debt (including amounts due within one year)(a)	[1]	35,659	34,813
Spent Nuclear Fuel Obligation, Noncurrent		813	732
Due to Related Parties, Noncurrent	[2]	677	667
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)	[1]	1,135	1,113
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Due to Related Parties, Noncurrent	[2]	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		2,048	1,267
Long-term debt (including amounts due within one year)(a)	[1]	32,562	31,741
Spent Nuclear Fuel Obligation, Noncurrent		813	732
Due to Related Parties, Noncurrent	[2]	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)	[1]	1,962	1,959
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Due to Related Parties, Noncurrent	[2]	677	667
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent		1,136	1,024
Deferred Finance Costs, Net		67	64
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		717	699
Long-term debt (including amounts due within one year)(a)	[1]	9,979	9,241
Spent Nuclear Fuel Obligation, Noncurrent		1,136	1,024
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		717	699
Long-term debt (including amounts due within one year)(a)	[1]	9,871	9,152
Spent Nuclear Fuel Obligation, Noncurrent		813	732
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)	[1]	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		717	699
Long-term debt (including amounts due within one year)(a)	[1]	8,200	7,482
Spent Nuclear Fuel Obligation, Noncurrent		813	732
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]	1,671	1,670
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		45	46
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		1	1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		365
Long-term debt (including amounts due within one year)(a)	[1]	7,035	7,033
Due to Related Parties, Noncurrent	[2]	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		365
Long-term debt (including amounts due within one year)(a)	[1]	7,615	7,585
Due to Related Parties, Noncurrent	[2]	218	215
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
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]	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		365
Long-term debt (including amounts due within one year)(a)	[1]	7,615	7,585
Due to Related Parties, Noncurrent	[2]	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
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]	218	215
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Due to Related Parties, Noncurrent		184	184
Deferred Finance Costs, Net		15	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)	[1]	2,580	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)	[1]	2,806	2,794
Due to Related Parties, Noncurrent		193	192
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)	[1]	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)	[1]	2,806	2,794
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)	[1]	0	0
Due to Related Parties, Noncurrent		193	192
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Due to Related Parties, Noncurrent		252	252
Deferred Finance Costs, Net		14	15
Baltimore Gas and Electric Company [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		6	6
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		95	45
Long-term debt (including amounts due within one year)(a)	[1]	2,323	2,322
Due to Related Parties, Noncurrent	[2]	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		95	45
Long-term debt (including amounts due within one year)(a)	[1]	2,501	2,467
Due to Related Parties, Noncurrent	[2]	266	260
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		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]	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		95	45
Long-term debt (including amounts due within one year)(a)	[1]	2,501	2,467
Due to Related Parties, Noncurrent	[2]	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)	[1]	0	0
Due to Related Parties, Noncurrent	[2]	266	260
Pepco Holdings LLC [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		2	2
Pepco Holdings LLC [Member] | Reported Value Measurement [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		167	522
Long-term debt (including amounts due within one year)(a)	[1]	5,860	5,898
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		167	522
Long-term debt (including amounts due within one year)(a)	[1]	5,801	5,809
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	0
Long-term debt (including amounts due within one year)(a)	[1]	0	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		167	522
Long-term debt (including amounts due within one year)(a)	[1]	5,510	5,520
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	0
Long-term debt (including amounts due within one year)(a)	[1]	291	289
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		29	30
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		167	23
Long-term debt (including amounts due within one year)(a)	[1]	2,350	2,349
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		167	23
Long-term debt (including amounts due within one year)(a)	[1]	2,813	2,796
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	0
Long-term debt (including amounts due within one year)(a)	[1]	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		167	23
Long-term debt (including amounts due within one year)(a)	[1]	2,804	2,788
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	0
Long-term debt (including amounts due within one year)(a)	[1]	9	8
Delmarva Power and Light Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		11	11
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)(a)	[1]	1,326	1,340
Delmarva Power and Light Company [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)	[1]	1,374	1,383
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]
Long-term debt (including amounts due within one year)(a)	[1]	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]
Long-term debt (including amounts due within one year)(a)	[1]	1,374	1,383
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]
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		5	6
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)(a)		1,145	1,155
Atlantic City Electric Company [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)		1,271	1,287
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]
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]
Long-term debt (including amounts due within one year)(a)		989	1,007
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]
Long-term debt (including amounts due within one year)(a)		$ 282	$ 280

[1] Includes unamortized debt issuance costs which are not fair valued of $199 million, $67 million, $45 million, $15 million, $14 million, $2 million, $29 million, $11 million, and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 31, 2017. Includes unamortized debt issuance costs of $200 million, $64 million, $46 million, $15 million, $15 million, $2 million, $30 million, $11 million, and $6 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of December 31, 2016.

[2] Includes unamortized debt issuance costs which are not fair valued of $7 million, $1 million, and $6 million for Exelon, ComEd and BGE, respectively, as of March 31, 2017 and December 31, 2016.