Supplemental Financial Information - Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2012		Oct. 31, 2000
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	$ 45.00
Other Investments [Abstract]
Total investments	766.00			3,055.00
Supplemental Financial Information Textuals [Abstract]
Payment to IRS	302.00		302.00
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Estimated residual value of leased assets	1,492.00			1,492.00		1,600.00
Less: unearned income	(836.00)			(807.00)
Net investment in long-term leases	656.00			685.00
Accrued Liabilities Current [Abstract]
Compensation-related accruals	520.00	[1]		708.00	[1]
Taxes accrued	297.00			353.00
Interest accrued	192.00			236.00
Severance accrued	15.00			91.00
Other accrued expenses	231.00			412.00	[2]
Total accrued expenses	1,255.00			1,800.00
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables	21.00			18.00
Property, Plant And Equipment [Abstract]
Accumulated depreciation	10,959.00	[3]		12,184.00	[3]
Accumulated amortization of nuclear fuel	1.00			2,078.00
Accounts receivable, net
Allowance for uncollectible accounts	(199.00)			(293.00)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges	488.00			367.00
Pension and non-pension postretirement benefit plans	(2,938.00)			(3,155.00)
Accumulated unrealized gain (loss) on marketable securities	0
Accumulated other comprehensive income (loss), net	(2,450.00)			(2,767.00)
Capital Leases Net Investment In Direct Financing Leases [Member]
Other Investments [Abstract]
Other Investments	656.00			685.00
Trust For Benefit Of Employees [Member]
Other Investments [Abstract]
Other Investments	65.00	[4]		100.00	[4]
Financing Trusts [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	15.00	[5]		22.00	[5]
NuStart Energy Development [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	1.00
Keystone Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	13.00			38.00
Conemaugh Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	16.00			26.00
CENG [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				1,849.00
Safe Harbor [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				293.00
Malacha [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				8.00
Sacramento Solar [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				34.00
Exelon Generation Co L L C [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	30.00			2,247.00
Other Investments [Abstract]
Total investments	41.00			2,269.00
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Net investment in long-term leases				693.00
Accrued Liabilities Current [Abstract]
Compensation-related accruals	264.00	[1]		371.00	[1]
Taxes accrued	241.00			247.00
Interest accrued	56.00			60.00
Severance accrued	9.00			42.00
Other accrued expenses	209.00			396.00	[2]
Total accrued expenses	779.00			1,116.00
Property, Plant And Equipment [Abstract]
Accumulated depreciation	5,313.00	[6]		6,014.00	[6]
Accumulated amortization of nuclear fuel	1,784.00
Accounts receivable, net
Allowance for uncollectible accounts	(29.00)			(84.00)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges	915.00			513.00
Pension and non-pension postretirement benefit plans				(19.00)
Accumulated other comprehensive income (loss), net	915.00			513.00
Exelon Generation Co L L C [Member] | Trust For Benefit Of Employees [Member]
Other Investments [Abstract]
Other Investments	11.00	[4]		22.00	[4]
Exelon Generation Co L L C [Member] | Financing Trusts [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	0	[5]
Exelon Generation Co L L C [Member] | NuStart Energy Development [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	1.00
Exelon Generation Co L L C [Member] | Keystone Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	13.00			38.00
Exelon Generation Co L L C [Member] | Conemaugh Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	16.00			26.00
Exelon Generation Co L L C [Member] | CENG [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				1,849.00
Exelon Generation Co L L C [Member] | Safe Harbor [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				293.00
Exelon Generation Co L L C [Member] | Malacha [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				8.00
Exelon Generation Co L L C [Member] | Sacramento Solar [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments				33.00
Commonwealth Edison Co [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	6.00			6.00
Other Investments [Abstract]
Total investments	27.00			14.00
Accrued Liabilities Current [Abstract]
Compensation-related accruals	127.00	[1]		125.00	[1]
Taxes accrued	59.00			61.00
Interest accrued	124.00			96.00
Severance accrued	2.00			4.00
Other accrued expenses	6.00			9.00
Total accrued expenses	318.00			295.00
Property, Plant And Equipment [Abstract]
Accumulated depreciation	2,750.00			2,998.00
Accounts receivable, net
Allowance for uncollectible accounts	(78.00)			(70.00)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges	0			0
Pension and non-pension postretirement benefit plans				0
Accumulated unrealized gain (loss) on marketable securities	(1.00)			0
Accumulated other comprehensive income (loss), net	(1.00)			0
Commonwealth Edison Co [Member] | Trust For Benefit Of Employees [Member]
Other Investments [Abstract]
Other Investments	21.00	[4]		8.00	[4]
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	6.00	[5]		6.00	[5]
Commonwealth Edison Co [Member] | NuStart Energy Development [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	0
Commonwealth Edison Co [Member] | Keystone Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	0
Commonwealth Edison Co [Member] | Conemaugh Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	0
PECO Energy Co [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	8.00			8.00
Other Investments [Abstract]
Total investments	30.00			30.00
Accrued Liabilities Current [Abstract]
Compensation-related accruals	48.00	[1]		45.00	[1]
Taxes accrued	5.00			3.00
Interest accrued	27.00			32.00
Severance accrued	1.00			1.00
Other accrued expenses	2.00			1.00
Total accrued expenses	83.00			82.00
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(17.00)			(15.00)
Property, Plant And Equipment [Abstract]
Accumulated depreciation	2,662.00			2,797.00
Accounts receivable, net
Allowance for uncollectible accounts	(92.00)			(99.00)
Accumulated Other Comprehensive Income (Loss) [Abstract]
Net unrealized gain (loss) on cash flow hedges	0			0
Pension and non-pension postretirement benefit plans	0			0
Accumulated other comprehensive income (loss), net	0			1.00
PECO Energy Co [Member] | Low Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(1.00)			(1.00)
PECO Energy Co [Member] | Medium Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(3.00)			(3.00)
PECO Energy Co [Member] | High Risk [Member]
Financing Receivable Recorded Investment [Line Items]
Installment plan receivables uncollectible accounts reserve	(13.00)			(11.00)
PECO Energy Co [Member] | Trust For Benefit Of Employees [Member]
Other Investments [Abstract]
Other Investments	22.00	[4]		22.00	[4]
PECO Energy Co [Member] | Financing Trusts [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	8.00	[5]		8.00	[5]
PECO Energy Co [Member] | NuStart Energy Development [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	0
PECO Energy Co [Member] | Keystone Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	0
PECO Energy Co [Member] | Conemaugh Fuels [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	0
Baltimore Gas and Electric Company [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	8.00			8.00
Other Investments [Abstract]
Total investments	8.00			13.00
Accrued Liabilities Current [Abstract]
Compensation-related accruals	42.00			38.00
Taxes accrued	26.00			22.00
Interest accrued	41.00			41.00
Severance accrued				5.00
Other accrued expenses	1.00
Total accrued expenses	110.00			106.00
Property, Plant And Equipment [Abstract]
Accumulated depreciation	2,466.00			2,595.00
Accounts receivable, net
Allowance for uncollectible accounts	(37.00)			(40.00)
Baltimore Gas and Electric Company [Member] | Trust For Benefit Of Employees [Member]
Other Investments [Abstract]
Other Investments				5.00
Baltimore Gas and Electric Company [Member] | Financing Trusts [Member]
Investments In Affiliates Subsidiaries Associates And Joint Ventures [Abstract]
Total equity method investments	$ 8.00			$ 8.00

[1] Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

[2] Includes $327 million and $184 million for amounts accrued related to Antelope Valley as of December 31, 2012 and December 31, 2011, respectively.

[3] Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,078 million and $1,784 million as of December 31, 2012 and 2011, respectively.

[4] The Registrants' investments in these marketable securities are recorded at fair market value.

[5] Includes investments in financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments in affiliates on the Consolidated Balance Sheets. See Note 1 - Significant Accounting Policies for additional information.

[6] Includes accumulated amortization of nuclear fuel in the reactor core of $2,078 million and $1,784 million as of December 31, 2012 and 2011, respectively.