Regulatory Matters - Schedule of Regulatory Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 310	$ 327
Noncurrent regulatory liabilities	4,550	4,388
Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	51	2
Noncurrent regulatory liabilities	37	43
Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	2,879	2,740
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	118	99
Noncurrent regulatory liabilities	1,448	1,423
Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25	53
Noncurrent regulatory liabilities	2	0
Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	1
Noncurrent regulatory liabilities	10	10
Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	32	21
Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8	20
Noncurrent regulatory liabilities	94	114
Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20	8
Noncurrent regulatory liabilities	29	37
Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	68	78
Noncurrent regulatory liabilities	16	0
Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	2	8
Noncurrent regulatory liabilities	0	0
Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3	38
Noncurrent regulatory liabilities	0	0
Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	12	16
Noncurrent regulatory liabilities	0	0
Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3	4
Noncurrent regulatory liabilities	3	0
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	125	170
Noncurrent regulatory liabilities	3,655	3,512
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	2,389	2,293
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	94	78
Noncurrent regulatory liabilities	1,249	1,219
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25	45
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3	9
Noncurrent regulatory liabilities	16	0
Commonwealth Edison Co [Member] | Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3	38
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Commonwealth Edison Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	1	0
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	90	106
Noncurrent regulatory liabilities	657	629
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
PECO Energy Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	490	447
PECO Energy Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	8
Noncurrent regulatory liabilities	2	0
PECO Energy Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	1
Noncurrent regulatory liabilities	10	10
PECO Energy Co [Member] | Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	32	21
PECO Energy Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8	20
Noncurrent regulatory liabilities	94	114
PECO Energy Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20	8
Noncurrent regulatory liabilities	29	37
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	58	58
Noncurrent regulatory liabilities	0	0
PECO Energy Co [Member] | Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	2	8
Noncurrent regulatory liabilities	0	0
PECO Energy Co [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
PECO Energy Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
PECO Energy Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	2	3
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	44	48
Noncurrent regulatory liabilities	200	204
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	24	21
Noncurrent regulatory liabilities	199	204
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0
Noncurrent regulatory liabilities	0
Baltimore Gas and Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	7	11
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	12	16
Noncurrent regulatory liabilities	0	0
Baltimore Gas and Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1	0
Noncurrent regulatory liabilities	1	0
Renewable Energy Program [Member] | Commonwealth Edison Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	16	9
Over Recovered Electric Energy And Transmission Costs [Member] | Commonwealth Edison Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 19