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Investment in Unconsolidated Affiliates Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Enable Midstream Partners [Member]
Related Party Transaction [Line Items]
Proceeds from Equity Method Investment, Distribution	$ 35.3	$ 35.3	$ 105.9	$ 105.9
Enable Midstream Partners [Member] \| OG&E [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	4.7	4.5	12.2	10.0
Operating Costs Charged [Member] \| Enable Midstream Partners [Member] \| OGE Energy [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	0.2	0.7	0.5	2.2
Employment Costs [Member] \| Enable Midstream Partners [Member] \| OGE Energy [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	5.3	6.2	22.1	23.5
Natural Gas Transportation [Member] \| Enable Midstream Partners [Member] \| OG&E [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	8.8	8.8	26.3	26.3
Natural Gas Purchases [Member] \| Enable Midstream Partners [Member] \| OG&E [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	0.1	$ 0.4	2.6	$ (0.4)
Excluding Fuel Purchases [Member]
Related Party Transaction [Line Items]
Accounts receivable - unconsolidated affiliates	$ 1.7		$ 1.7		$ 2.0