Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Mar. 31, 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		1,151	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]	1,654	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	34,108	34,264
Due to Related Parties, Noncurrent	[4]	389	389
Spent Nuclear Fuel Obligation, Noncurrent		1,151	1,147
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	1,654	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	34,984	36,705
Due to Related Parties, Noncurrent	[4]	421	431
Spent Nuclear Fuel Obligation, Noncurrent		922	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]	1,654	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	33,091	34,735
Due to Related Parties, Noncurrent	[4]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		922	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]	1,893	1,970
Due to Related Parties, Noncurrent	[4]	421	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		1,151	1,147
Deferred Finance Costs, Net		57	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]	166	2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,965	8,990
Spent Nuclear Fuel Obligation, Noncurrent		1,151	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]	166	2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	9,195	9,512
Spent Nuclear Fuel Obligation, Noncurrent		922	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	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]	166	2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,585	7,839
Spent Nuclear Fuel Obligation, Noncurrent		922	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	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,610	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		60	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]	317
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,694	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]	317
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,061	8,418
Due to Related Parties, Noncurrent	[4]	222	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]	317
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,061	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]	222	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]	220
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,723	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]	220
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,870	3,194
Long-term debt to financing trust	[4]	199	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]	220
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,870	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]	0	0
Long-term debt to financing trust	[4]	199	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]	45	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]	45	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,689
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]	45	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,689
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] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		6	6
Pepco Holdings LLC [Member] | Reported Value Measurement [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	407	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,849	5,874
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]	407	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,706	6,019
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	[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] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	407	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,423	5,722
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	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	283	297
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		32	32
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	60	26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,540	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]	60	26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,942	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	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]	60	26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,933	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	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	9	9
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]
Short-term Debt, Fair Value	[1]	211	216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,296	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]	211	216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,320	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	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]	211	216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,320	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	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		5	5
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	136	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,114	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]	136	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,190	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]	136	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	916	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]	$ 274	$ 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, $57 million, $60 million, $20 million, $16 million, $6 million, $32 million, $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 31, 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 and government-backed fixed rate non-recourse debt.

[4] Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of March 31, 2018 and December 31, 2017.