Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		$ 533	$ 460
Long-term debt (including amounts due within one year) (a)		275	333
Due to Related Parties, Noncurrent	[1]	641	641
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
Debt Issuance Cost		180	150
Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Cost		7
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		536	463
Long-term debt (including amounts due within one year) (a)		25,145	21,014
Due to Related Parties, Noncurrent		641	641
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		536	463
Long-term debt (including amounts due within one year) (a)		25,924	22,936
Due to Related Parties, Noncurrent		673	648
SNF obligation		818	833
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]
Lines of Credit, Fair Value Disclosure		3
Long-term debt (including amounts due within one year) (a)		931
Due to Related Parties, Noncurrent		0
SNF obligation		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]
Lines of Credit, Fair Value Disclosure		533
Long-term debt (including amounts due within one year) (a)		23,644
Due to Related Parties, Noncurrent		0
SNF obligation		818
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]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		1,349
Due to Related Parties, Noncurrent		673
SNF obligation		0
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		29	36
Long-term debt (including amounts due within one year) (a)		127	146
Due to Related Parties, Noncurrent		933	943
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
Debt Issuance Cost		70	70
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		29	36
Long-term debt (including amounts due within one year) (a)		8,959	8,196
Spent Nuclear Fuel Obligation, Noncurrent		1,021	1,021
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]
Lines of Credit, Fair Value Disclosure		29	36
Long-term debt (including amounts due within one year) (a)		9,116	8,822
SNF obligation		818	833
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]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
SNF obligation		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]
Lines of Credit, Fair Value Disclosure		29
Long-term debt (including amounts due within one year) (a)		7,767
SNF obligation		818
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]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		1,349
SNF obligation		0
Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		294	304
Due to Related Parties, Noncurrent		205	205
Debt Issuance Cost		38	33
Commonwealth Edison Co [Member] | Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Cost		1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		294	304
Long-term debt (including amounts due within one year) (a)		6,509	5,925
Due to Related Parties, Noncurrent		205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lines of Credit, Fair Value Disclosure		294	304
Long-term debt (including amounts due within one year) (a)		7,069	6,788
Due to Related Parties, Noncurrent		213	213
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]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		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]
Lines of Credit, Fair Value Disclosure		294
Long-term debt (including amounts due within one year) (a)		7,069
Due to Related Parties, Noncurrent		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]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		213
PECO Energy Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Related Parties, Noncurrent		184	184
Debt Issuance Cost		15	14
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)		2,580	2,232
Due to Related Parties, Noncurrent		184	184
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)		2,786	2,537
Due to Related Parties, Noncurrent		195	199
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)		0
Due to Related Parties, Noncurrent		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)		2,786
Due to Related Parties, Noncurrent		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)		0
Due to Related Parties, Noncurrent		195
Baltimore Gas and Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt		210	120
Long-term debt (including amounts due within one year) (a)			1,932
Due to Related Parties, Noncurrent		252	252
Debt Issuance Cost		9	10
Baltimore Gas and Electric Company [Member] | Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Cost		6
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		213	123
Long-term debt (including amounts due within one year) (a)		1,858
Due to Related Parties, Noncurrent		252
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]
Lines of Credit, Fair Value Disclosure		213	123
Long-term debt (including amounts due within one year) (a)		2,044	2,178
Due to Related Parties, Noncurrent		264	$ 236
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]
Lines of Credit, Fair Value Disclosure		3
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		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]
Lines of Credit, Fair Value Disclosure		210
Long-term debt (including amounts due within one year) (a)		2,044
Due to Related Parties, Noncurrent		0
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]
Lines of Credit, Fair Value Disclosure		0
Long-term debt (including amounts due within one year) (a)		0
Due to Related Parties, Noncurrent		$ 264

[1] Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.