Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Variable Interest Entity [Line Items]
Current Assets	$ 1,185	[1],[2]	$ 1,271	[1]
Non Current Assets	7,676	[1],[2]	7,580	[1]
Total Assets	8,861	[1],[2]	8,851	[1]
Current Liabilities	520	[1],[2]	611	[1]
Non Current Liabilities	2,812	[1],[2]	2,730	[1]
Total Liabilities	3,332	[1],[2]	3,341	[1]
Assets	87,391		86,814		86,814
Total liabilities	62,753	[3]	62,681	[3]
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets	8,182		8,160
Total liabilities	2,702		2,723
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current Assets	1,134	[2]	1,242
Non Current Assets	7,664	[2]	7,566
Total Assets	8,798	[2]	8,808
Current Liabilities	434	[2]	526
Non Current Liabilities	2,682	[2]	2,600
Total Liabilities	3,116	[2]	3,126
Assets	45,318	[4]	45,348	[4]
Total liabilities	32,150	[4]	31,297	[4]
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets	8,118		8,119
Total liabilities	2,486		2,507
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Current Assets	46		21
Non Current Assets	3		3
Total Assets	49		24
Current Liabilities	80		77
Non Current Liabilities	120		120
Total Liabilities	200		197
Assets	8,130		8,078
Total liabilities	5,307	[5]	5,325	[5]
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets	49		24
Total liabilities	$ 200		$ 197

[1] Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

[2] .

[3] Exelon’s consolidated assets include $8,182 million and $8,160 million at March 31, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $2,702 million and $2,723 million at March 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 - Variable Interest Entities.

[4] Generation’s consolidated assets include $8,118 million and $8,119 million at March 31, 2015 and December 31, 2014, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $2,486 million and $2,507 million at March 31, 2015 and December 31, 2014, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 - Variable Interest Entities.

[5] BGE’s consolidated assets include $49 million and $24 million at March 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $200 million and $197 million at March 31, 2015 and December 31, 2014, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 3 — Variable Interest Entities.