Supplemental Financial Information - Balance Sheet (Details) (USD $)	3 Months Ended				12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2010	Dec. 31, 2013		Dec. 31, 2012
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Equity Method Investments	$ 1,910,000,000					$ 1,925,000,000
Supplemental Financial Information Textuals [Abstract]
Payment to IRS					302,000,000
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Estimated residual value of leased assets	731,000,000					1,465,000,000
Less: unearned income	(363,000,000)					(767,000,000)
Net investment in long-term leases	368,000,000					698,000,000
CapitalLeaseNetInvestmentInDirectFinancingLeasesPrepaymentsReceived	1,200,000,000
Utilities Operating Expense Maintenance And Operations [Abstract]
Operating and maintenance	1,858,000,000		1,764,000,000
Accrued Liabilities Current [Abstract]
Taxes accrued	285,000,000
Total accrued expenses	1,364,000,000					1,633,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation	14,066,000,000	[1]				13,713,000,000	[2]
Accumulated amortization of nuclear fuel	2,425,000,000					2,371,000,000
Accounts receivable, net
Allowance for uncollectible accounts	306,000,000					272,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net	(2,036,000,000)	[3]	(2,673,000,000)	[3]		(2,040,000,000)	[3]	(2,767,000,000)	[3]
Capital Leases, Net Investment in Direct Financing Leases, Initial Direct Costs	1,600,000,000
CPS Board San Antonio, Texas | EquipmentLeasedToOtherPartyMember
Utilities Operating Expense Maintenance And Operations [Abstract]
Cash Proceeds from Direct Finance Lease Contract Termination	335,000,000		0
Exelon Generation Co L L C [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Equity Method Investments	1,910,000,000					1,925,000,000
Utilities Operating Expense Maintenance And Operations [Abstract]
Operating and maintenance	938,000,000		965,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses	831,000,000					976,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation	7,245,000,000	[1]				7,034,000,000	[2]
Accumulated amortization of nuclear fuel	2,425,000,000					2,371,000,000
Accounts receivable, net
Allowance for uncollectible accounts	46,000,000					57,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net	193,000,000	[3]	409,000,000	[3]		214,000,000	[3]	513,000,000	[3]
Exelon Generation Co L L C [Member] | CPS Board San Antonio, Texas | EquipmentLeasedToOtherPartyMember
Utilities Operating Expense Maintenance And Operations [Abstract]
Operating and maintenance	1,000,000
Cash Proceeds from Direct Finance Lease Contract Termination	335,000,000
Capital Leases Written Off	336,000,000
Commonwealth Edison Co [Member]
Utilities Operating Expense Maintenance And Operations [Abstract]
Operating and maintenance	287,000,000		292,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses	214,000,000					307,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation	3,247,000,000					3,184,000,000
Accounts receivable, net
Allowance for uncollectible accounts	76,000,000					62,000,000
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net	0					0
PECO Energy Co [Member]
Utilities Operating Expense Maintenance And Operations [Abstract]
Operating and maintenance	256,000,000		164,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses	137,000,000					106,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation	2,958,000,000					2,935,000,000
Accounts receivable, net
Allowance for uncollectible accounts	140,000,000					107,000,000
Installment plan receivables	18,000,000					19,000,000
Installment plan receivables uncollectible accounts reserve	(15,000,000)					(18,000,000)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated other comprehensive income (loss), net	1,000,000	[3]	1,000,000	[3]		1,000,000	[3]	1,000,000	[3]
PECO Energy Co [Member] | Low To Medium Risk [Member]
Accounts receivable, net
Installment plan receivables uncollectible accounts reserve	(1,000,000)					(1,000,000)
PECO Energy Co [Member] | Medium Risk [Member]
Accounts receivable, net
Installment plan receivables uncollectible accounts reserve	(4,000,000)					(4,000,000)
PECO Energy Co [Member] | High Risk [Member]
Accounts receivable, net
Installment plan receivables uncollectible accounts reserve	(10,000,000)					(13,000,000)
Baltimore Gas and Electric Company [Member]
Utilities Operating Expense Maintenance And Operations [Abstract]
Operating and maintenance	163,000,000		124,000,000
Accrued Liabilities Current [Abstract]
Total accrued expenses	111,000,000					111,000,000
Property, Plant And Equipment [Abstract]
Accumulated depreciation	2,741,000,000					2,702,000,000
Accounts receivable, net
Allowance for uncollectible accounts	$ 44,000,000					$ 46,000,000

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $2,425 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $2,371 million.

[3] (a) All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.