Summary of Significant Accounting Policies Depreciation and Amortization (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Provision for Depreciation Rate	2.80%	2.80%
Projected Provision for Depreciation in Next Fiscal Year	2.80%
Percent Of Intangible Plant Balance Amortizable	96.00%
Percent of Intangible Plant Balance Amortizable Thereafter	4.00%
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