XML 33 R31.htm IDEA: XBRL DOCUMENT v2.4.0.8
Regulatory Liabilities (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Sep. 30, 2013
Regulatory Liabilities [Line Items]      
Regulatory Liabilities $ 13.0 $ 9.7 $ 11.4
Regulatory Tracker Mechanisms
     
Regulatory Liabilities [Line Items]      
Regulatory Liabilities $ 13.0 $ 9.7 $ 11.4