Regulatory Matters - Schedule of Regulatory Assets (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Feb. 28, 2010
Regulatory Assets [Line Items]
Current regulatory assets	$ 847		$ 760
Noncurrent regulatory assets	6,076		5,910
Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Current regulatory assets	247		221
Noncurrent regulatory assets	3,009		2,794
Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Current regulatory assets	6		10
Noncurrent regulatory assets	1,536		1,459
AMI Expenses [Member]
Regulatory Assets [Line Items]
Current regulatory assets	25		5
Noncurrent regulatory assets	271		159
AMI Meter Events [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			5
Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	251		178
Noncurrent regulatory assets	120		285
Debt Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	8		12
Noncurrent regulatory assets	49		56
Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Current regulatory assets	7		0
Noncurrent regulatory assets	183		219
Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Current regulatory assets	4		12
Noncurrent regulatory assets	8		0
Severance [Member]
Regulatory Assets [Line Items]
Current regulatory assets			16
Noncurrent regulatory assets			12
Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Current regulatory assets	1		1
Noncurrent regulatory assets	115		102
MGP Remediation Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	36		40
Noncurrent regulatory assets	221		212
RTO Startup Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets			2
Noncurrent regulatory assets			0
Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	67		48
Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Current regulatory assets	20		17
Noncurrent regulatory assets	187		176
Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	37		53
Noncurrent regulatory assets	11		9
Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	1		3
Noncurrent regulatory assets	2		3
Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Current regulatory assets	10		13
Noncurrent regulatory assets	20		30
Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Current regulatory assets	75		71
Noncurrent regulatory assets	85		154
Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	89		73
Noncurrent regulatory assets	159		148
Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	2		2
Noncurrent regulatory assets	6		9
Conservation Voltage Reductio [Member]
Regulatory Assets [Line Items]
Current regulatory assets	1
Noncurrent regulatory assets	1
Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Current regulatory assets	7
Noncurrent regulatory assets	0
Other Assets [Member]
Regulatory Assets [Line Items]
Current regulatory assets	20	[1]	31	[1]
Noncurrent regulatory assets	26	[1]	30	[1]
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Current regulatory assets	349		329
Noncurrent regulatory assets	852		933
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Commonwealth Edison Co [Member] | Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		2
Noncurrent regulatory assets	64		65
Commonwealth Edison Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Current regulatory assets	10		5
Noncurrent regulatory assets	81		35
Commonwealth Edison Co [Member] | AMI Meter Events [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	251		178
Noncurrent regulatory assets	120		285
Commonwealth Edison Co [Member] | Debt Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	6		9
Noncurrent regulatory assets	47		53
Commonwealth Edison Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Commonwealth Edison Co [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
Commonwealth Edison Co [Member] | Severance [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		12
Noncurrent regulatory assets	0		0
Commonwealth Edison Co [Member] | Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Current regulatory assets	1		1
Noncurrent regulatory assets	73		67
Commonwealth Edison Co [Member] | MGP Remediation Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	30		33
Noncurrent regulatory assets	189		178
Commonwealth Edison Co [Member] | RTO Startup Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets			2
Noncurrent regulatory assets			0
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	67		48
Commonwealth Edison Co [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Current regulatory assets	20		17
Noncurrent regulatory assets	187		176
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	26		52
Noncurrent regulatory assets	7		6
Commonwealth Edison Co [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Commonwealth Edison Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Commonwealth Edison Co [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Commonwealth Edison Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Commonwealth Edison Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Regulatory assets	7		6
Commonwealth Edison Co [Member] | Conservation Voltage Reductio [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0
Noncurrent regulatory assets	0
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Current regulatory assets
Noncurrent regulatory assets
Commonwealth Edison Co [Member] | Other Assets [Member]
Regulatory Assets [Line Items]
Current regulatory assets	5	[1]	18	[1]
Noncurrent regulatory assets	17	[1]	20	[1]
Commonwealth Edison Co [Member] | Purchase of Receivable Program [Member]
Regulatory Assets [Line Items]
Regulatory assets	14		27
Commonwealth Edison Company [Member]
Regulatory Assets [Line Items]
Electric Transmission Costs Under-Recovery	3
Commonwealth Edison Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	33		58
Electric Transmission Costs Under-Recovery	22		17
Commonwealth Edison Company [Member] | Under-Recovered Electric Supply Costs [Member]
Regulatory Assets [Line Items]
Electric Transmission Costs Under-Recovery	4		35
Commonwealth Edison Company [Member] | Over Recovered Electric Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Liabilities	19
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Current regulatory assets	29		17
Noncurrent regulatory assets	1,529		1,448
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	1,400		1,317
PECO Energy Co [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Current regulatory assets	15		0
Noncurrent regulatory assets	62		58
PECO Energy Co [Member] | AMI Meter Events [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			5
PECO Energy Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Debt Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	2		3
Noncurrent regulatory assets	2		3
PECO Energy Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
PECO Energy Co [Member] | Severance [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
PECO Energy Co [Member] | Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	26		25
PECO Energy Co [Member] | MGP Remediation Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	6		6
Noncurrent regulatory assets	31		33
PECO Energy Co [Member] | RTO Startup Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
PECO Energy Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
PECO Energy Co [Member] | Conservation Voltage Reductio [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0
Noncurrent regulatory assets	0
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0
Noncurrent regulatory assets	0
PECO Energy Co [Member] | Other Assets [Member]
Regulatory Assets [Line Items]
Current regulatory assets	6	[1]	8	[1]
Noncurrent regulatory assets	8	[1]	7	[1]
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Current regulatory assets	214		181
Noncurrent regulatory assets	510		524
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Baltimore Gas and Electric Company [Member] | Deferred Income Taxes [Member]
Regulatory Assets [Line Items]
Current regulatory assets	6		8
Noncurrent regulatory assets	72		77
Baltimore Gas and Electric Company [Member] | AMI Expenses [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	128		66
Baltimore Gas and Electric Company [Member] | AMI Meter Events [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
Baltimore Gas and Electric Company [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Baltimore Gas and Electric Company [Member] | Debt Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	1		1
Noncurrent regulatory assets	8		8
Baltimore Gas and Electric Company [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Baltimore Gas and Electric Company [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
Baltimore Gas and Electric Company [Member] | Severance [Member]
Regulatory Assets [Line Items]
Current regulatory assets	4		4
Noncurrent regulatory assets	8		12
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligations [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	16		10
Baltimore Gas and Electric Company [Member] | MGP Remediation Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		1
Noncurrent regulatory assets	1		1
Regulatory assets	1		1
Baltimore Gas and Electric Company [Member] | RTO Startup Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
Baltimore Gas and Electric Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Current regulatory assets			0
Noncurrent regulatory assets			0
Baltimore Gas and Electric Company [Member] | Renewable Energy And Associated REC [Member]
Regulatory Assets [Line Items]
Current regulatory assets	0		0
Noncurrent regulatory assets	0		0
Baltimore Gas and Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	11		1
Noncurrent regulatory assets	4		3
Regulatory assets	15		4
Baltimore Gas and Electric Company [Member] | Under Recovered Electric Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	10
Baltimore Gas and Electric Company [Member] | Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	1		3
Noncurrent regulatory assets	2		3
Regulatory assets					16
Baltimore Gas and Electric Company [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Assets [Line Items]
Current regulatory assets	10		13
Noncurrent regulatory assets	20		30
Regulatory assets	28		37
Baltimore Gas and Electric Company [Member] | Rate Stabilization Deferral [Member]
Regulatory Assets [Line Items]
Current regulatory assets	75		71
Noncurrent regulatory assets	85		154
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	89		73
Noncurrent regulatory assets	159		148
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Current regulatory assets	2		2
Noncurrent regulatory assets	6		9
Regulatory assets	4		3
Baltimore Gas and Electric Company [Member] | Conservation Voltage Reductio [Member]
Regulatory Assets [Line Items]
Current regulatory assets	1
Noncurrent regulatory assets	1
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Current regulatory assets	7
Noncurrent regulatory assets	0
Baltimore Gas and Electric Company [Member] | Other Assets [Member]
Regulatory Assets [Line Items]
Current regulatory assets	7	[1]	4	[1]
Noncurrent regulatory assets	0	[1]	3	[1]
Baltimore Gas and Electric Company [Member] | Purchase of Receivable Program [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 7		$ 0

[1] For ComEd and BGE, includes Purchase of Receivable Program regulatory assets. As of December 31, 2014, ComEd and BGE had a regulatory asset related to the Purchase of Receivable Program of $14 million and $7 million, respectively. As of December 31, 2013, ComEd and BGE had a regulatory asset related to the Purchase of Receivable Program of $27 million and $0 million, respectively.