Short-Term Debt and Credit Facilities (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Short-term debt		$ 0.0	$ 168.4
Line of Credit Facility [Abstract]
Aggregate Commitment		900.0
Long-term Line of Credit	[1]	$ 0.3
Weighted Average Interest Rate		1.05%
OGE Energy [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	[2]	$ 450.0
Line of Credit Facility [Abstract]
Long-term Line of Credit	[1],[2]	$ 0.0
Weighted Average Interest Rate	[2],[3]	0.00%
Maturity	[2],[4]	Mar. 08, 2023
OG&E [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	[5]	$ 450.0
Line of Credit Facility [Abstract]
Letters of Credit Outstanding, Amount	[1],[5]	$ 0.3
Weighted Average Interest Rate	[3],[5]	1.05%
Maturity	[4],[5]	Mar. 08, 2023
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

[1] Includes direct borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit at September 30, 2018.

[2] This bank facility is available to back up the Company's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility.

[3] Represents the weighted-average interest rate for the outstanding borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit.

[4] In March 2017, the Company and OG&E entered into unsecured five-year revolving credit agreements totaling $900.0 million ($450.0 million for the Company and $450.0 million for OG&E). Each of the facilities contained an option, which could be exercised up to two times, to extend the term of the respective facility for an additional year. Effective March 9, 2018, the Company and OG&E utilized one of those extensions to extend the maturity of their respective credit facility from March 8, 2022 to March 8, 2023.

[5] This bank facility is available to back up OG&E's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility.