Fair Value Measurements Carrying and Fair Value Amounts (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
OG&E Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-Term Debt, Carrying Amount	$ 2,509.9	$ 2,509.7
Long-Term Debt, Fair Value	2,811.6	2,957.7
OG&E Industrial Authority Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-Term Debt, Carrying Amount	135.4	135.4
Long-Term Debt, Fair Value	135.4	135.4
OG&E Tinker Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-Term Debt, Carrying Amount	10.1	10.2
Long-Term Debt, Fair Value	9.1	10.3
OGE Energy Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-Term Debt, Carrying Amount	100.0	100.0
Long-Term Debt, Fair Value	$ 99.9	$ 99.9