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Investment in Unconsolidated Affiliates Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Enable Midstream Partners [Member] \| OG&E [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	$ 4.5	$ 4.7	$ 12.1	$ 12.2
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	0.1	0.2	0.3	0.5
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	3.6	5.3	20.0	22.1
Natural Gas Transportation [Member] \| Enable Midstream Partners [Member] \| OG&E [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	9.4	8.8	33.5	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	(1.1)	$ 0.1	(5.4)	$ 2.6
Excluding Fuel Purchases [Member]
Related Party Transaction [Line Items]
Accounts receivable - unconsolidated affiliates	$ 0.9		$ 0.9		$ 1.7