Income Taxes - Reconciliation to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%	[1]
State income taxes, net of Federal income tax benefit	1.30%	4.80%	(3.50%)	[1]
Qualified nuclear decommissioning trust fund income	(2.40%)	(3.70%)	(5.40%)	[1]
Tax exempt income	0.20%	0.20%	0.20%	[1]
Domestic production activities deduction	2.00%	0.00%	0.00%	[1]
Health care reform legislation	(0.10%)	(0.10%)	(0.10%)	[1]
Amortization of investment tax credit, net deferred taxes	1.10%	1.90%	1.10%	[1]
Plant basis differences	(1.90%)	(1.60%)	(2.20%)	[1]
Merger expenses			2.60%	[1],[2]
Merger expenses (c)			2.40%	[1]
Statute of limitations expiration	(2.60%)	(0.10%)	(0.10%)	[1]
Production tax credits and other credits	(2.40%)	(2.10%)	(2.40%)	[1]
Non-controlling interest	(1.80%)
Other	0.00%	0.10%	1.10%	[1]
Effective income tax rate	26.80%	37.60%	34.90%	[1]
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%	[1]
State income taxes, net of Federal income tax benefit	(1.90%)	1.80%	4.90%	[1]
Qualified nuclear decommissioning trust fund income	(4.80%)	(6.10%)	(9.10%)	[1]
Tax exempt income	0.50%	0.30%	0.40%	[1]
Domestic production activities deduction	4.10%	0.00%	0.00%	[1]
Health care reform legislation	0.00%	0.00%	0.00%	[1]
Amortization of investment tax credit, net deferred taxes	2.00%	3.00%	1.30%	[1]
Plant basis differences	0.00%	0.00%	(3.70%)	[1]
Merger expenses			4.40%	[1],[2]
Merger expenses (c)			0.00%	[1]
Statute of limitations expiration	(5.30%)	(0.20%)	(0.30%)	[1]
Production tax credits and other credits	(4.80%)	(3.40%)	0.00%	[1]
Non-controlling interest	(3.70%)
Other	0.60%	(0.70%)	0.40%	[1]
Effective income tax rate	16.90%	36.70%	47.30%	[1]
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of Federal income tax benefit	4.50%	3.40%	4.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Tax exempt income	0.00%	0.00%	0.00%
Domestic production activities deduction	0.00%	0.00%	0.00%
Health care reform legislation	(0.20%)	(0.70%)	(0.40%)
Amortization of investment tax credit, net deferred taxes	0.30%	0.60%	0.40%
Plant basis differences	(0.10%)	(0.80%)	0.00%
Merger expenses			0.00%	[2]
Merger expenses (c)			0.00%
Statute of limitations expiration	0.00%	0.00%	0.00%
Production tax credits and other credits	0.00%	(0.10%)	(0.30%)
Non-controlling interest	0.00%
Other	(0.30%)	(0.30%)	0.60%
Effective income tax rate	39.60%	37.90%	38.70%
PECO Energy Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of Federal income tax benefit	(0.10%)	1.60%	2.00%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Tax exempt income	0.00%	0.00%	0.00%
Domestic production activities deduction	0.00%	0.00%	0.00%
Health care reform legislation	0.00%	0.00%	0.00%
Amortization of investment tax credit, net deferred taxes	0.10%	0.10%	0.30%
Plant basis differences	(10.40%)	(7.10%)	0.00%
Merger expenses			0.00%	[2]
Merger expenses (c)			0.00%
Statute of limitations expiration		0.00%	0.00%
Production tax credits and other credits	0.00%	0.00%	(11.50%)
Non-controlling interest	0.00%
Other	(0.10%)	0.30%	0.20%
Effective income tax rate	24.50%	29.10%	25.00%
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate	35.00%	35.00%	35.00%	[3]
State income taxes, net of Federal income tax benefit	5.00%	4.90%	24.30%	[3]
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	[3]
Tax exempt income	0.00%	0.00%	0.00%	[3]
Domestic production activities deduction	0.00%	0.00%	0.00%	[3]
Health care reform legislation	(0.20%)	(0.20%)	(11.60%)	[3]
Amortization of investment tax credit, net deferred taxes	0.30%	0.00%	8.60%	[3]
Plant basis differences	0.20%	(0.20%)	0.00%	[3]
Merger expenses			0.00%	[2],[3]
Merger expenses (c)			24.20%	[3]
Statute of limitations expiration	0.00%	0.00%	0.00%	[3]
Production tax credits and other credits	0.00%	0.00%	(9.00%)	[3]
Non-controlling interest	0.00%
Other	0.20%	0.90%	13.90%	[3]
Effective income tax rate	39.90%	39.00%	63.60%	[3]

[1] Exelon activity for the twelve months ended December 31, 2012 includes the results of Constellation and BGE for March 12, 2012—December 31, 2012. Generation activity for the twelve months ended December 31, 2012 includes the results of Constellation for March 12, 2012—December 31, 2012.

[2] Prior to the close of the merger, the Registrants recorded the applicable taxes on merger transaction costs assuming the merger would not be completed. Upon closing of the merger, the Registrants reversed such taxes for those merger transaction costs that were determined to be non tax-deductible upon successful completion of a merger.

[3] BGE activity represents the activity for the twelve months ended December 31, 2012.