Summary of Significant Accounting Policies Depreciation and Amortization (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Provision for Depreciation Rate	2.70%	2.50%
Projected provision for depreciation in next fiscal year	2.70%
Percent Of Intangible Plant Balance Amortizable	98.70%
Percent of Intangible Plant Balance Amortizable Thereafter	1.30%
Transmission Equipment [Member] | OG&E [Member]
Amount of Acquisition Adjustments	$ 3.3
Redbud Plant [Member]
Amount of Acquisition Adjustments	$ 148.3	$ 148.3