CONSOLIDATED STATEMENTS OF CAPITALIZATION - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Common stock, par value $0.01 per share; authorized 450.0 shares; and outstanding 200.1 shares and 199.7 shares, respectively	$ 2.0	$ 2.0
Premium on common stock	1,129.3	1,125.7
Retained earnings	3,036.1	2,906.3
Accumulated other comprehensive loss, net of tax	(27.9)	(28.9)
Total stockholders' equity	4,139.5	4,005.1
Unamortized debt expense	(24.2)	(22.9)
Total long-term debt	3,195.2	3,146.9
Less: long-term debt due within one year	0.0	(250.0)
Total long-term debt (excluding long-term debt due within one year)	3,195.2	2,896.9
Total capitalization (including long-term debt due within one year)	7,334.7	7,152.0
Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized discount	(10.5)	(10.2)
Senior Notes [Member] \| Series Due January 15, 2019 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 0.0	250.0
Debt Instrument, Interest Rate, Stated Percentage	8.25%
Senior Notes [Member] \| Series Due July 15, 2027 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 125.0	125.0
Debt Instrument, Interest Rate, Stated Percentage	6.65%
Senior Notes [Member] \| Series Due April 15, 2028 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 100.0	100.0
Debt Instrument, Interest Rate, Stated Percentage	6.50%
Senior Notes [Member] \| Series Due August 15, 2028 [Member] [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 400.0	400.0
Debt Instrument, Interest Rate, Stated Percentage	3.80%
Senior Notes [Member] \| Series Due March 15, 2030 \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 300.0	0.0
Debt Instrument, Interest Rate, Stated Percentage	3.30%
Senior Notes [Member] \| Series Due January 15, 2036 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 110.0	110.0
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Senior Notes [Member] \| Series Due February 1, 2038 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 200.0	200.0
Debt Instrument, Interest Rate, Stated Percentage	6.45%
Senior Notes [Member] \| Series Due June 1, 2040 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 250.0	250.0
Debt Instrument, Interest Rate, Stated Percentage	5.85%
Senior Notes [Member] \| Series Due May 15, 2041 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 250.0	250.0
Debt Instrument, Interest Rate, Stated Percentage	5.25%
Senior Notes [Member] \| Series Due May 1, 2043 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 250.0	250.0
Debt Instrument, Interest Rate, Stated Percentage	3.90%
Senior Notes [Member] \| Series Due March 15, 2044 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 250.0	250.0
Debt Instrument, Interest Rate, Stated Percentage	4.55%
Senior Notes [Member] \| Series Due December 15, 2044 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 250.0	250.0
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Senior Notes [Member] \| Series due August 15, 2047 [Member] [Domain] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 300.0	300.0
Debt Instrument, Interest Rate, Stated Percentage	3.85%
Senior Notes [Member] \| Series due April 1, 2047 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 300.0	300.0
Debt Instrument, Interest Rate, Stated Percentage	4.15%
Long-term Debt [Member] \| Due August 31, 2062 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 9.5	9.6
Debt Instrument, Interest Rate, Stated Percentage	3.80%
Debentures Subject to Mandatory Redemption [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Total long-term debt	$ 135.4
Debentures Subject to Mandatory Redemption [Member] \| Garfield Industrial Authority Bond [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	47.0	47.0
Debentures Subject to Mandatory Redemption [Member] \| Muskogee Industrial Authority Bond Due 2025 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	32.4	32.4
Debentures Subject to Mandatory Redemption [Member] \| Muskogee Industrial Authority Bond Due 2027 [Member] \| Og and E [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Long-term Debt, Gross	$ 56.0	$ 56.0

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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