Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		$ 389	$ 389
Spent Nuclear Fuel Obligation, Noncurrent		1,157	1,147
Deferred Finance Costs, Net		213	201
Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		1
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	1,252	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	34,337	34,264
Due to Related Parties, Noncurrent	[4]	389	389
Spent Nuclear Fuel Obligation, Noncurrent		1,157	1,147
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	1,252	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	34,542	36,705
Due to Related Parties, Noncurrent	[4]	420	431
Spent Nuclear Fuel Obligation, Noncurrent		921	936
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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Due to Related Parties, Noncurrent	[4]	0	0
Spent Nuclear Fuel Obligation, 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	[1]	1,252	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	32,388	34,735
Due to Related Parties, Noncurrent	[4]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		921	936
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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,154	1,970
Due to Related Parties, Noncurrent	[4]	420	431
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent		1,157	1,147
Deferred Finance Costs, Net		55	60
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]		2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,886	8,990
Spent Nuclear Fuel Obligation, Noncurrent		1,157	1,147
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]		2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,993	9,512
Spent Nuclear Fuel Obligation, Noncurrent		921	936
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	[1]		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	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	[1]		2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,461	7,839
Spent Nuclear Fuel Obligation, Noncurrent		921	936
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	[1]		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,532	1,673
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Commonwealth Edison Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		205	205
Deferred Finance Costs, Net		59	52
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	[1]	320
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,695	7,601
Due to Related Parties, Noncurrent	[4]	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	[1]	320
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,865	8,418
Due to Related Parties, Noncurrent	[4]	219	227
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	[1]	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Due to Related Parties, Noncurrent	[4]	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	[1]	320
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,865	8,418
Due to Related Parties, Noncurrent	[4]	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	[1]	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Due to Related Parties, Noncurrent	[4]	219	227
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		184	184
Deferred Finance Costs, Net		20	17
PECO Energy Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	50
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,773	2,903
Long-term debt to financing trust	[4]	184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	50
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,869	3,194
Long-term debt to financing trust	[4]	201	204
PECO Energy 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)(b)(c)	[2],[3]	0	0
Long-term debt to financing trust	[4]	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]
Short-term Debt, Fair Value	[1]	50
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,819	3,194
Long-term debt to financing trust	[4]	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]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	50	0
Long-term debt to financing trust	[4]	201	204
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		16	17
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	136	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,578
Long-term debt to financing trust	[2],[3]		2,577
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	[1]	136	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,629
Long-term debt to financing trust	[2],[3]		2,825
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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0
Long-term debt to financing trust	[2],[3]		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	[1]	136	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,629
Long-term debt to financing trust	[2],[3]		2,825
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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0
Long-term debt to financing trust	[2],[3]		0
Pepco Holdings LLC [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		12	6
Pepco Holdings LLC [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	247	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	6,116	5,874
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	247	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,872	6,019
Pepco Holdings LLC [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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Pepco Holdings LLC [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]	247	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,300	5,722
Pepco Holdings LLC [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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	572	297
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		35	32
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]		26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,631	2,540
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]		26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,970	3,123
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	[1]		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	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	[1]		26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,863	3,114
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	[1]		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	107	9
Delmarva Power and Light Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		12	11
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]		216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,494	1,300
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	[1]		216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,491	1,393
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	[1]		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	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	[1]		216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,295	1,393
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	[1]		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	196	0
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		4	5
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	247	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,107	1,121
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	247	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,167	1,237
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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	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	[1]	247	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	898	949
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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	$ 269	$ 288

[1] Level 1 securities consist of dividends payable (included in other current liabilities). Level 2 securities consist of short term borrowings.

[2] Includes unamortized debt issuance costs which are not fair valued of $213 million, $55 million, $59 million, $20 million, $16 million, $12 million, $35 million, $12 million and $4 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of June 30, 2018. Includes unamortized debt issuance costs which are not fair valued of $201 million, $60 million, $52 million, $17 million, $17 million, $6 million, $32 million, $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of December 31, 2017.

[3] Level 2 securities consist of fixed-rate taxable debt securities, fixed-rate tax-exempt debt, variable rate tax-exempt debt and variable rate non-recourse debt. Level 3 securities consist of fixed-rate private placement taxable debt securities, fixed rate nonrecourse debt, government-backed fixed rate non-recourse debt and loan agreements.

[4] Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of June 30, 2018