Summary of Significant Accounting Policies - Average Depreciation Rates (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Natural gas distribution | Delmarva
Property, Plant and Equipment [Line Items]
Average depreciation rates	2.70%	2.50%	2.50%
Natural gas distribution | Florida
Property, Plant and Equipment [Line Items]
Average depreciation rates	3.30%	3.20%	3.50%
Natural gas transmission
Property, Plant and Equipment [Line Items]
Average depreciation rates	2.70%	2.70%	2.60%
Electric distribution | Florida
Property, Plant and Equipment [Line Items]
Average depreciation rates	3.60%	3.80%	4.20%