Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)		$ 795	$ 865
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Debt Issuance Costs, Net		216	201
Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		0	(1)
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		714	929
Long-term debt (including amounts due within one year)(a)	[1]	35,869	36,705
Due to Related Parties, Noncurrent	[2]	400	431
Spent Nuclear Fuel Obligation, Noncurrent		949	936
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		714	929
Long-term debt (including amounts due within one year)(a)	[1]	33,711	34,735
Due to Related Parties, Noncurrent	[2]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		949	936
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	2,158	1,970
Due to Related Parties, Noncurrent	[2]	400	431
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		714	929
Long-term debt (including amounts due within one year)(a)	[1]	35,424	34,264
Due to Related Parties, Noncurrent	[2]	390	389
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)		91	103
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Debt Issuance Costs, Net		51	60
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			2
Long-term debt (including amounts due within one year)(a)	[1]	8,910	9,512
Spent Nuclear Fuel Obligation, Noncurrent		949	936
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			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]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			2
Long-term debt (including amounts due within one year)(a)	[1]	7,467	7,839
Spent Nuclear Fuel Obligation, Noncurrent		949	936
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			0
Long-term debt (including amounts due within one year)(a)	[1]	1,443	1,673
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			2
Long-term debt (including amounts due within one year)(a)	[1]	8,793	8,990
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		63	52
Commonwealth Edison Co [Member] | Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		(1)	(1)
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	8,390	8,418
Due to Related Parties, Noncurrent	[2]	209	227
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	8,390	8,418
Due to Related Parties, Noncurrent	[2]	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]	209	227
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	8,101	7,601
Due to Related Parties, Noncurrent	[2]	205	205
PECO Energy Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		23	17
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	3,207	3,194
Due to Related Parties, Noncurrent		191	204
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	3,157	3,194
Due to Related Parties, Noncurrent		0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	50	0
Due to Related Parties, Noncurrent		191	204
PECO Energy Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	3,084	2,903
Due to Related Parties, Noncurrent		184	184
Baltimore Gas and Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		18	17
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		35	77
Long-term debt (including amounts due within one year)(a)	[1]	2,950	2,825
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		35	77
Long-term debt (including amounts due within one year)(a)	[1]	2,950	2,825
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		35	77
Long-term debt (including amounts due within one year)(a)	[1]	2,876	2,577
Pepco Holdings LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)		633	686
Pepco Holdings LLC [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		14	6
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		179	350
Long-term debt (including amounts due within one year)(a)	[1]	6,101	6,019
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		179	350
Long-term debt (including amounts due within one year)(a)	[1]	5,436	5,722
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	665	297
Pepco Holdings LLC [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		179	350
Long-term debt (including amounts due within one year)(a)	[1]	6,259	5,874
Potomac Electric Power Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		34	32
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		40	26
Long-term debt (including amounts due within one year)(a)	[1]	3,097	3,123
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		40	26
Long-term debt (including amounts due within one year)(a)	[1]	2,901	3,114
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	196	9
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		40	26
Long-term debt (including amounts due within one year)(a)	[1]	2,719	2,540
Delmarva Power & Light Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		12	11
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			216
Long-term debt (including amounts due within one year)(a)	[1]	1,496	1,393
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			216
Long-term debt (including amounts due within one year)(a)	[1]	1,303	1,393
Delmarva Power & Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			0
Long-term debt (including amounts due within one year)(a)	[1]	193	0
Delmarva Power & Light Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value			216
Long-term debt (including amounts due within one year)(a)	[1]	1,494	1,300
Atlantic City Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		7	5
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		139	108
Long-term debt (including amounts due within one year)(a)	[1]	1,262	1,237
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		139	108
Long-term debt (including amounts due within one year)(a)	[1]	987	949
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	275	288
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		139	108
Long-term debt (including amounts due within one year)(a)	[1]	$ 1,188	$ 1,121

[1] Includes unamortized debt issuance costs which are not fair valued of $216 million, $51 million, $63 million, $23 million, $18 million, $14 million, $34 million, $12 million and $7 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 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.

[2] Includes unamortized debt issuance costs which are not fair valued of $0 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2018. Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2017.