Summary of Significant Accounting Policies Depreciation and Amortization (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Provision for Depreciation Rate	2.90%	2.80%
Projected Provision for Depreciation in Next Fiscal Year	2.90%
Percent Of Intangible Plant Balance Amortizable	96.40%
Percent of Intangible Plant Balance Amortizable Thereafter	3.60%
Current Fiscal Year End Date	--12-31
Transmission Equipment [Member] | OG&E [Member]
Amount of Acquisition Adjustments	$ 3.3
Redbud Plant [Member]
Amount of Acquisition Adjustments	$ 148.3	$ 148.3