Short-Term Debt and Credit Facility Short-Term Debt and Credit Facility (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Advances from parent	$ 49.9	$ 0.0
Advances to parent	0.0	$ 333.6
OG&E [Member]
Line of Credit Facility [Line Items]
Intercompany Borrowings, Maximum Borrowing Capacity	$ 400.0
Intercompany Borrowing Agreement, Expiration Date	Dec. 13, 2018
Line of Credit Facility, Maximum Borrowing Capacity	$ 400.0
Letters of Credit Outstanding, Amount	$ 1.8
Short-term Debt, Weighted Average Interest Rate	0.95%
Line of Credit Facility, Amount Outstanding	$ 0.0
Commercial Paper	0.0
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