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Short-Term Debt and Credit Facilities (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Short-term Debt [Line Items]    
Advances to parent $ 340.9 $ 215.6
OG&E [Member]    
Short-term Debt [Line Items]    
Intercomany Borrowings, Maximum Borrowing Capacity 400.0  
Outstanding Intercompany Borrowings 0.0  
Aggregate Commitment - Revolving Credit Facility 400.0  
Letters of Credit Outstanding $ 1.9  
Weighted Average Interest Rate 0.95%  
Short Term Borrowing Capacity That Has Regulatory Approval $ 800.0  
Period For Which Regulatory Approval Has Been Given to Acquire Short Term Debt 2 years