Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Mar. 31, 2017 USD ($)
Guarantor Obligations [Line Items]
Other Commitment	$ 3,212
Guarantor Obligations, Maximum Exposure, Undiscounted	48
Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	1,527
Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	628
Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	1,038
GuaranteedLeaseResidualValues [Member]
Guarantor Obligations [Line Items]
Other Commitment	19
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Other Commitment	2,404
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	1,440
Exelon Generation Co L L C [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	0
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	964
Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	219
Commonwealth Edison Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	14
Commonwealth Edison Co [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	200
Commonwealth Edison Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	5
PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Other Commitment	208
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	23
PECO Energy Co [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	178
PECO Energy Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	7
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	266
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	5
Baltimore Gas and Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	250
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	11
PEPCO Holdings Inc [Member]
Guarantor Obligations [Line Items]
Other Commitment	36
PEPCO Holdings Inc [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	1
PEPCO Holdings Inc [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	0
PEPCO Holdings Inc [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	16
PEPCO Holdings Inc [Member] | GuaranteedLeaseResidualValues [Member]
Guarantor Obligations [Line Items]
Other Commitment	19
Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	15
Guarantor Obligations, Maximum Exposure, Undiscounted	14
Potomac Electric Power Company [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	1
Potomac Electric Power Company [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	0
Potomac Electric Power Company [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	9
Potomac Electric Power Company [Member] | GuaranteedLeaseResidualValues [Member]
Guarantor Obligations [Line Items]
Other Commitment	5
Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	8
Guarantor Obligations, Maximum Exposure, Undiscounted	13
Atlantic City Electric Company [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	3
Atlantic City Electric Company [Member] | GuaranteedLeaseResidualValues [Member]
Guarantor Obligations [Line Items]
Other Commitment	5
Delmarva Power and Light Company [Member]
Guarantor Obligations [Line Items]
Other Commitment	11
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Delmarva Power and Light Company [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Other Commitment	0
Delmarva Power and Light Company [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Other Commitment	0
Delmarva Power and Light Company [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Other Commitment	4
Delmarva Power and Light Company [Member] | GuaranteedLeaseResidualValues [Member]
Guarantor Obligations [Line Items]
Other Commitment	$ 7