Debt and Credit Agreements - Schedule of Long-term Debt Maturities (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
2017		$ 2,075
2018		959
2019		3,564
2020		1,513
2021		3,084
Thereafter	[1]	22,852
Total		34,047
Total long-term debt to financing trusts		390	$ 648
Long-term Debt, Gross		33,657	33,311
ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		206	206
PECO Financing Trusts [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		184
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
2017		346
2018		615
2019		2,144
2020		1
2021		1,024
Thereafter		4,825
Total		8,955
Long-term Debt, Gross		8,955	9,208
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
2017		840
2018		300
2019		500
2020		350
2021		0
Thereafter	[2]	5,892
Total		7,882
Total long-term debt to financing trusts		206	206
Long-term Debt, Gross		7,676	7,101
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		206	206
PECO Energy Co [Member]
Debt Instrument [Line Items]
2017		500
2018		0
2019		0
2020		300
2021		350
Thereafter	[3]	1,959
Total		3,109
Long-term Debt, Gross		2,925	2,600
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
2017		0
2018		0
2019		0
2020		300
2021		250
Thereafter		2,050
Total		2,600
Total long-term debt to financing trusts		0	258
Long-term Debt, Gross		2,600	2,341
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
2017		383
2018		44
2019		20
2020		262
2021		310
Thereafter		4,170
Total		5,189
Long-term Debt, Gross		5,189	5,157
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
2017		19
2018		14
2019		0
2020		2
2021		310
Thereafter		2,225
Total		2,570
Long-term Debt, Gross		2,570	2,381
Delmarva Power and Light Company [Member]
Debt Instrument [Line Items]
2017		83
2018		12
2019		0
2020		0
2021		0
Thereafter		1,214
Total		1,309
Long-term Debt, Gross		1,309	1,348
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
2017		281
2018		18
2019		20
2020		260
2021		0
Thereafter		548
Total		1,127
Long-term Debt, Gross		$ 1,127	$ 1,162

[1] Includes $390 million due to ComEd and PECO financing trusts.

[2] Includes $206 million due to ComEd financing trust.

[3] Includes $184 million due to PECO financing trusts.