Impairment of Long-lived Assets - Narrative (Details) - USD ($)					12 Months Ended
		May. 31, 2014	Feb. 26, 2014	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2000	Oct. 31, 2000
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges					$ 24,000,000
Interest costs incurred	[1],[2],[3]				1,170,000,000	$ 1,144,000,000	$ 1,423,000,000
Estimated residual value of leased assets					639,000,000	685,000,000			$ 1,600,000,000
Capital lease net investment in direct financing leases prepayments received								$ 1,200,000,000.0
Proceeds from termination of direct financing lease investment			$ 335,000,000		0	335,000,000	0
Capital leases net investment in direct financing leases writeoff			$ 336,000,000
Pre Tax Loss						1,000,000
Exelon Generation Co L L C [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Carrying amount of long lived assets to be written down		$ 151,000,000		$ 75,000,000		1,000,000,000
Fair value of impaired assets		65,000,000		32,000,000		556,000,000
Impairment charges		$ 86,000,000		$ 43,000,000		450,000,000
Utilities Operating Expense, Impairments							111,000,000
Interest costs incurred	[1],[2],[3]				445,000,000	419,000,000	411,000,000
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Interest costs incurred							8,000,000
Baltimore Gas and Electric Company [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Interest costs incurred	[1],[2]				113,000,000	118,000,000	$ 129,000,000
Constellation Energy Group LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges					$ 5,000,000	$ 124,000,000

[1] .

[2] Includes interest expense to affiliates.

[3] On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, the 2014 financial results include CENG’s financial position and results of operations beginning April 1, 2014.