OGE Energy (OGE) 10-K 27 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2019	Jun. 30, 2019
Document Information [Line Items]
Entity Registrant Name	OGE ENERGY CORP.
Entity Central Index Key	0001021635
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	200,177,358	200,175,812
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$ 8,519,482,559
Entity Incorporation, State or Country Code	OK
Entity Tax Identification Number	73-1481638
Entity Address, Address Line One	321 North Harvey
Entity Address, Address Line Two	P.O. Box 321
Trading Symbol	OGE
Security Exchange Name	NYSE
Entity Interactive Data Current	Yes
City Area Code	405
Local Phone Number	553-3000
Entity Address, State or Province	OK
Entity Address, Postal Zip Code	73101-0321
Entity File Number	1-12579
Title of 12(b) Security	Common Stock
Entity Address, City or Town	Oklahoma City
Share Price		$ 42.56
Document Transition Report	false
Document Annual Report	true

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,175.5		$ 2,211.7		$ 0
Revenues from Alternative Revenue Programs	56.1		58.6		0
OPERATING REVENUES
Total operating revenues	2,231.6		2,270.3		2,261.1
Total cost of sales	786.9		892.5		897.6
OPERATING EXPENSES
Other operation and maintenance	491.8		474.6		458.7
Depreciation and amortization	355		321.6		283.5
Taxes other than income	93.6		92		89.4
Operating expenses	940.4		888.2		831.6
Operating income (loss)	504.3		489.6		531.9
OTHER INCOME (EXPENSE)
Equity in earnings of unconsolidated affiliates	113.9		152.8		131.2
Allowance for equity funds used during construction	4.5		23.8		39.7
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	(9.8)		(10.8)		(21.6)
Other income	21.9		21.7		46.4
Other expense	(23.5)		(23.4)		(14.1)
Net other income	107		164.1		181.6
INTEREST EXPENSE
Interest on long-term debt	138.3		157.4		153.6
Allowance for borrowed funds used during construction	(2.8)		(11.7)		(18)
Interest on short-term debt and other interest charges	12.4		10.3		8.2
Interest expense	147.9		156		143.8
INCOME BEFORE TAXES	463.4		497.7		569.7
INCOME TAX EXPENSE (BENEFIT)	29.8		72.2		(49.3)	[1]
NET INCOME	$ 433.6		$ 425.5		$ 619
BASIC AVERAGE COMMON SHARES OUTSTANDING	200.1		199.7		199.7
DILUTED AVERAGE COMMON SHARES OUTSTANDING	200.7		200.5		200
BASIC EARNINGS PER AVERAGE COMMON SHARE	$ 2.17	[2]	$ 2.13	[2]	$ 3.10
DILUTED EARNINGS PER AVERAGE COMMON SHARE	2.16	[2]	2.12	[2]	3.10
DIVIDENDS DECLARED PER COMMON SHARE	$ 1.5050		$ 1.3950		$ 1.2700
[1]	The Company recorded an income tax benefit of $245.2 million and income tax expense of $10.5 million during the fourth quarter of 2017 due to the Company remeasuring deferred taxes related to the natural gas midstream operations and other operations segments, respectively, as a result of the 2017 Tax Act.
[2]	Due to the impact of dilution on the earnings per share calculation, quarterly earnings per share amounts may not add to the total.

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 433.6	$ 425.5	$ 619
Pension Plan and Restoration of Retirement Income Plan:
Amortization of deferred net loss, net of tax of $1.1, $1.1 and $1.4, respectively	3.4	3.3	2.5
Amortization of prior service credit, net of tax of $0.0, $0.0 and $0.0, respectively	0	0	0.1
Net gain (loss) arising during the period, net of tax of $(2.6), ($4.7) and $0.2, respectively	(8.3)	(14.1)	0.4
Settlement cost, net of tax of $2.7, $1.6 and $1.4, respectively	8.6	4.7	2.2
Postretirement Benefit Plans:
Amortization of prior service credit, net of tax of ($0.6), ($0.6) and ($0.3), respectively	(1.7)	(1.7)	(0.6)
Amortization of deferred net gain, net of tax of $0.0, $0.0 and $0.0, respectively	(0.2)	0	0
Prior service cost arising during the period, net of tax of $0.0, $0.0 and $4.0, respectively	0	0	6.3
Net gain (loss) arising during the period, net of tax of ($0.1), $0.7 and ($0.2), respectively	(0.2)	2.1	(0.6)
Settlement cost, net of tax of $0.0, $0.0 and $0.2, respectively	0	0	0.5
Other comprehensive income (loss), net of tax	1	(5.7)	10.6
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	0.6	0	0
Comprehensive income	$ 434.6	$ 419.8	$ 629.6

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Parenthetical - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan and Restoration of Retirement Income Plan:
Amortization of deferred net loss, net of tax of $1.1, $1.1 and $1.4, respectively	$ 1.1	$ 1.1	$ 1.4
Net gain (loss) arising during the period, net of tax of $(2.6), ($4.7) and $0.2, respectively	(2.6)	(4.7)	0.2
Amortization of prior service credit, net of tax of $0.0, $0.0 and $0.0, respectively	0	0	0
Postretirement plans:
Prior service cost arising during the period, net of tax of $0.0, $0.0 and $4.0, respectively	0	0	4
Amortization of deferred net gain, net of tax of $0.0, $0.0 and $0.0, respectively	0	0	0
Net gain (loss) arising during the period, net of tax of ($0.1), $0.7 and ($0.2), respectively	(0.1)	0.7	(0.2)
Amortization of prior service credit, net of tax of ($0.6), ($0.6) and ($0.3), respectively	(0.6)	(0.6)	(0.3)
Amortization of deferred interest rate swap hedging losses, net of tax of $0, $0 and $0.0, respectively	0	0	0
Pension Plans [Member]
Pension Plan and Restoration of Retirement Income Plan:
Settlement cost, net of tax of $2.7, $1.6 and $1.4, respectively	2.7	1.6	1.4
Other Postretirement Benefits Plan [Member]
Pension Plan and Restoration of Retirement Income Plan:
Settlement cost, net of tax of $2.7, $1.6 and $1.4, respectively	$ 0	$ 0
Postretirement plans:
Settlement cost, net of tax of $0.0, $0.0 and $0.2, respectively			$ 0.2

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 433.6	$ 425.5	$ 619
Adjustments to reconcile net income to net cash provided from operating activities:
Depreciation and amortization	355	321.6	283.5
Deferred income taxes and investment tax credits, net	27.6	78.5	(50)
Equity in earnings of unconsolidated affiliates	(113.9)	(152.8)	(131.2)
Distributions from unconsolidated affiliates	125.5	141.2	131.2
Allowance for equity funds used during construction	(4.5)	(23.8)	(39.7)
Stock-based compensation expense	13.9	13.4	9.1
Regulatory assets	47.1	10.8	(3.7)
Regulatory liabilities	(45.6)	(16.5)	(3.7)
Other assets	(3.8)	6.2	(0.7)
Other liabilities	19.2	1	(65.5)
Change in certain current assets and liabilities:
Accounts receivable and accrued unbilled revenues, net	18.8	19.8	(21.8)
Income taxes receivable	(1)	(4.1)	13.6
Fuel, materials and supplies inventories	4.2	27.3	(3.6)
Fuel recoveries	(33)	(3.4)	53
Other current assets	5.1	25.1	27.2
Accounts payable	(34.5)	29.7	27.1
Other current liabilities	(38)	73.2	(66.7)
Net cash provided from operating activities	681.5	951.1	784.5
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures (less allowance for equity funds used during construction)	(635.5)	(573.6)	(824.1)
Investment in unconsolidated affiliates	(7.7)	(2.5)	(8.5)
Return of capital - unconsolidated affiliates	18.5	0	10
Proceeds from sale of assets	0	0.1	0.7
Net cash used in investing activities	(624.7)	(576)	(821.9)
CASH FLOWS FROM FINANCING ACTIVITIES
Increase (decrease) in short-term debt	112	(168.4)	(67.8)
Proceeds from long-term debt	296.5	396	592.1
Payment of long-term debt	(250.1)	(250.1)	(225.1)
Dividends paid on common stock	(299.2)	(272.2)	(247.6)
Cash paid for employee equity-based compensation and expense of common stock	(10.3)	(0.5)	(0.1)
Net cash provided from (used in) financing activities	(151.1)	(295.2)	51.5
NET CHANGE IN CASH AND CASH EQUIVALENTS	(94.3)	79.9	14.1
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	94.3	14.4	0.3
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 0	$ 94.3	$ 14.4

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 0	$ 94.3
Accounts receivable, less reserve of $1.5 and $1.7, respectively	153.8	174.7
Accrued unbilled revenues	64.7	62.6
Income taxes receivable	10.9	9.9
Fuel inventories	46.3	57.6
Materials and supplies, at average cost	90.6	126.7
Fuel clause under recoveries	39.5	2
Other	24.4	29.5
Total current assets	430.2	557.3
OTHER PROPERTY AND INVESTMENTS
Investment in unconsolidated affiliates	1,151.5	1,177.5
Other	82.7	73.4
Total other property and investments	1,234.2	1,250.9
PROPERTY, PLANT AND EQUIPMENT
In service	12,771.1	11,994.8
Construction work in progress	141.6	376.4
Total property, plant and equipment	12,912.7	12,371.2
Less: accumulated depreciation	3,868.1	3,727.4
Net property, plant and equipment	9,044.6	8,643.8
DEFERRED CHARGES AND OTHER ASSETS
Regulatory assets	306	285.8
Other	9.3	10.8
Total deferred charges and other assets	315.3	296.6
TOTAL ASSETS	11,024.3	10,748.6
CURRENT LIABILITIES
Short-term debt	112	0
Accounts payable	194.9	239.3
Dividends payable	77.6	72.9
Customer deposits	83	83.6
Accrued taxes	41.9	44
Accrued interest	37.9	44.5
Accrued compensation	40.6	47.8
Long-term debt due within one year	0	250
Fuel clause over recoveries	4.8	0.3
Other	65.2	87
Total current liabilities	657.9	869.4
LONG-TERM DEBT	3,195.2	2,896.9
DEFERRED CREDITS AND OTHER LIABILITIES
Accrued benefit obligations	225	225.7
Deferred income taxes	1,375.8	1,310.9
Accumulated Deferred Investment Tax Credit	7.1	7.2
Regulatory liabilities	1,223.5	1,270.7
Other	200.3	162.7
Total deferred credits and other liabilities	3,031.7	2,977.2
Total liabilities	6,884.8	6,743.5
COMMITMENTS AND CONTINGENCIES (NOTE 15)
STOCKHOLDERS' EQUITY
Common stockholders' equity	1,131.3	1,127.7
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
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 11,024.3	$ 10,748.6

CONSOLIDATED BALANCE SHEETS Par

CONSOLIDATED BALANCE SHEETS Parenthetical - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts Receivable	$ 1.5	$ 1.7

CONSOLIDATED STATEMENTS OF CAPI

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	$ 2
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	(250)
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
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	250
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	125
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	100
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	400
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
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	110
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	200
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	250
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	250
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	250
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	250
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	250
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	300
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	300
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	47
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	$ 56

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CAPITALIZATION (Parenthetical) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	450	450
Common Stock, Shares, Outstanding	200.1	199.7
Debt Instrument, Maturity Date	Mar. 15, 2030
Garfield Industrial Authority, January 1, 2025 [Member]
Debt Instrument, Maturity Date	Jan. 1, 2025
Muskogee Industrial Authority, Janaury 1, 2025 [Member]
Debt Instrument, Maturity Date	Jan. 1, 2025
Muskogee Industrial Authority, June 1, 2027 [Member]
Debt Instrument, Maturity Date	Jun. 1, 2027
Senior Notes [Member] | Series Due January 15, 2019 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Jan. 15, 2019
Debt Instrument, Interest Rate, Stated Percentage	8.25%
Senior Notes [Member] | Series Due July 15, 2027 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Jul. 15, 2027
Debt Instrument, Interest Rate, Stated Percentage	6.65%
Senior Notes [Member] | Series Due April 15, 2028 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Apr. 15, 2028
Debt Instrument, Interest Rate, Stated Percentage	6.50%
Senior Notes [Member] | Series Due August 15, 2028 [Member] [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Aug. 15, 2028
Debt Instrument, Interest Rate, Stated Percentage	3.80%
Senior Notes [Member] | Series Due March 15, 2030 | OG&E [Member]
Debt Instrument, Maturity Date	Mar. 15, 2030
Debt Instrument, Interest Rate, Stated Percentage	3.30%
Senior Notes [Member] | Series Due January 15, 2036 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Jan. 15, 2036
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Senior Notes [Member] | Series Due February 1, 2038 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Feb. 1, 2038
Debt Instrument, Interest Rate, Stated Percentage	6.45%
Senior Notes [Member] | Series Due June 1, 2040 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Jun. 1, 2040
Debt Instrument, Interest Rate, Stated Percentage	5.85%
Senior Notes [Member] | Series Due May 15, 2041 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	May 15, 2041
Debt Instrument, Interest Rate, Stated Percentage	5.25%
Senior Notes [Member] | Series Due May 1, 2043 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	May 1, 2043
Debt Instrument, Interest Rate, Stated Percentage	3.90%
Senior Notes [Member] | Series Due March 15, 2044 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Mar. 15, 2044
Debt Instrument, Interest Rate, Stated Percentage	4.55%
Senior Notes [Member] | Series Due December 15, 2044 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Dec. 15, 2044
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Senior Notes [Member] | Series due April 1, 2047 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Apr. 1, 2047
Debt Instrument, Interest Rate, Stated Percentage	4.15%
Senior Notes [Member] | Series due August 15, 2047 [Member] [Domain] | OG&E [Member]
Debt Instrument, Maturity Date	Aug. 15, 2047
Debt Instrument, Interest Rate, Stated Percentage	3.85%
Long-term Debt [Member] | Due August 31, 2062 [Member] | OG&E [Member]
Debt Instrument, Maturity Date	Aug. 31, 2062
Debt Instrument, Interest Rate, Stated Percentage	3.80%
Minimum [Member] | Debentures Subject to Mandatory Redemption [Member] | Garfield Industrial Authority, January 1, 2025 [Member]
Debt Instrument, Interest Rate, Stated Percentage	1.20%
Minimum [Member] | Debentures Subject to Mandatory Redemption [Member] | Muskogee Industrial Authority, Janaury 1, 2025 [Member]
Debt Instrument, Interest Rate, Stated Percentage	1.19%
Minimum [Member] | Debentures Subject to Mandatory Redemption [Member] | Muskogee Industrial Authority, June 1, 2027 [Member]
Debt Instrument, Interest Rate, Stated Percentage	1.20%
Maximum [Member] | Debentures Subject to Mandatory Redemption [Member] | Garfield Industrial Authority, January 1, 2025 [Member]
Debt Instrument, Interest Rate, Stated Percentage	2.50%
Maximum [Member] | Debentures Subject to Mandatory Redemption [Member] | Muskogee Industrial Authority, Janaury 1, 2025 [Member]
Debt Instrument, Interest Rate, Stated Percentage	2.35%
Maximum [Member] | Debentures Subject to Mandatory Redemption [Member] | Muskogee Industrial Authority, June 1, 2027 [Member]
Debt Instrument, Interest Rate, Stated Percentage	2.48%

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Premium on Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Common Stock, Shares, Outstanding		199.7
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0
Balance at Dec. 31, 2016	$ 3,443.8	$ 2	$ 1,103.8	$ 2,367.3	$ (29.3)
Comprehensive income (loss)
Net income	619	$ 0	0	619	0
Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification, Number of Shares		0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0
Other comprehensive income, net of tax	10.6	$ 0	0	0	10.6
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	22.3	$ 0	0	26.8	(4.5)
Dividends, Common Stock, Cash, Number of Shares		0
Dividends declared on common stock	(253.6)	$ 0	0	(253.6)	0
Stock Issued During Period, Shares, New Issues		0
Expense of common stock	(0.1)	$ 0	(0.1)	0	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0
Stock-based compensation	9.1	$ 0	9.1	0	0
Balance at Dec. 31, 2017	$ 3,851.1	$ 2	1,112.8	2,759.5	(23.2)
Comprehensive income (loss)
DIVIDENDS DECLARED PER COMMON SHARE	$ 1.2700
Common Stock, Shares, Outstanding		199.7
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0
Net income	$ 425.5	$ 0	0	425.5	0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0
Other comprehensive income, net of tax	(5.7)	$ 0	0	0	(5.7)
Dividends, Common Stock, Cash, Number of Shares		0
Dividends declared on common stock	(278.7)	$ 0	0	(278.7)	0
Stock Issued During Period, Shares, New Issues		0
Expense of common stock	(0.1)	$ 0	(0.1)	0	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0
Stock-based compensation	13	$ 0	13	0	0
Balance at Dec. 31, 2018	$ 4,005.1	$ 2	1,125.7	2,906.3	(28.9)
Comprehensive income (loss)
DIVIDENDS DECLARED PER COMMON SHARE	$ 1.3950
Common Stock, Shares, Outstanding	199.7	199.7
Net Income (Loss), Including portion attributable to noncontrolling interest, Number of Shares		0
Net income	$ 433.6	$ 0	0	433.6	0
Other Comprehensive Income (Loss), Net of Tax, Number of Shares		0
Other comprehensive income, net of tax	1	$ 0	0	0	1
Dividends, Common Stock, Cash, Number of Shares		0
Dividends declared on common stock	(303.8)	$ 0	0	(303.8)	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Number of Shares		0.4
Stock-based compensation	3.6	$ 0	3.6	0	0
Balance at Dec. 31, 2019	$ 4,139.5	$ 2	$ 1,129.3	$ 3,036.1	$ (27.9)
Comprehensive income (loss)
DIVIDENDS DECLARED PER COMMON SHARE	$ 1.5050
Common Stock, Shares, Outstanding	200.1	200.1

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	Summary of Significant Accounting Policies Organization The Company is a holding company with investments in energy and energy services providers offering physical delivery and related services for both electricity and natural gas primarily in the south central U.S. The Company conducts these activities through two business segments: (i) electric utility and (ii) natural gas midstream operations. The accounts of the Company and its wholly-owned subsidiaries are included in the Consolidated Financial Statements. All intercompany transactions and balances are eliminated in consolidation. The Company generally uses the equity method of accounting for investments where its ownership interest is between 20 percent and 50 percent and it lacks the power to direct activities that most significantly impact economic performance. The electric utility segment generates, transmits, distributes and sells electric energy in Oklahoma and western Arkansas. Its operations are conducted through OG&E and are subject to regulation by the OCC, the APSC and the FERC. OG&E was incorporated in 1902 under the laws of the Oklahoma Territory and is a wholly-owned subsidiary of the Company. OG&E is the largest electric utility in Oklahoma, and its franchised service territory includes Fort Smith, Arkansas and the surrounding communities. OG&E sold its retail natural gas business in 1928 and is no longer engaged in the natural gas distribution business. The natural gas midstream operations segment represents the Company's investment in Enable through wholly-owned subsidiaries and ultimately OGE Holdings. Enable is primarily engaged in the business of gathering, processing, transporting and storing natural gas. Enable's natural gas gathering and processing assets are strategically located in four states and serve natural gas production in the Anadarko, Arkoma and Ark-La-Tex Basins. Enable also owns crude oil gathering assets in the Anadarko and Williston Basins. Enable has intrastate natural gas transportation and storage assets that are located in Oklahoma as well as interstate assets that extend from western Oklahoma and the Texas Panhandle to Louisiana, from Louisiana to Illinois and from Louisiana to Alabama. Enable's general partner is equally controlled by the Company and CenterPoint, who each have 50 percent management ownership. Based on the 50/50 management ownership, with neither company having control, the Company accounts for its interest in Enable using the equity method of accounting. The Company charges operating costs to OG&E and Enable based on several factors. Operating costs directly related to OG&E and Enable are assigned as such. Operating costs incurred for the benefit of OG&E and Enable are allocated either as overhead based primarily on labor costs or using the "Distrigas" method. The "Distrigas" method is a three-factor formula that uses an equal weighting of payroll, net operating revenues and gross property, plant and equipment. The Company adopted this method as a result of a recommendation by the OCC Staff. The Company believes this method provides a reasonable basis for allocating common expenses. Use of Estimates In preparing the Consolidated Financial Statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and contingent liabilities at the date of the Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Changes to these assumptions and estimates could have a material effect on the Company's Consolidated Financial Statements. However, the Company believes it has taken reasonable positions where assumptions and estimates are used in order to minimize the negative financial impact to the Company that could result if actual results vary from the assumptions and estimates. In management's opinion, the areas of the Company where the most significant judgment is exercised include the determination of Pension Plan assumptions, income taxes, contingency reserves, asset retirement obligations and depreciable lives of property, plant and equipment. For the electric utility segment, significant judgment is also exercised in the determination of regulatory assets and liabilities and unbilled revenues. Cash and Cash Equivalents For purposes of the Consolidated Financial Statements, the Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. These investments are carried at cost, which approximates fair value. Allowance for Uncollectible Accounts Receivable Customer balances are generally written off if not collected within six months after the final billing date. The allowance for uncollectible accounts receivable for OG&E is calculated by multiplying the last six months of electric revenue by the provision rate, which is based on a 12-month historical average of actual balances written off. To the extent the historical collection rates are not representative of future collections, there could be an effect on the amount of uncollectible expense recognized. Also, a portion of the uncollectible provision related to fuel within the Oklahoma jurisdiction is being recovered through the fuel adjustment clause. The allowance for uncollectible accounts receivable is a reduction to Accounts Receivable in the Consolidated Balance Sheets and is included in Other Operation and Maintenance Expense in the Consolidated Statements of Income. The allowance for uncollectible accounts receivable was $1.5 million and $1.7 million at December 31, 2019 and 2018, respectively. New business customers are required to provide a security deposit in the form of cash, bond or irrevocable letter of credit that is refunded when the account is closed. New residential customers whose outside credit scores indicate an elevated risk are required to provide a security deposit that is refunded based on customer protection rules defined by the OCC and the APSC. The payment behavior of all existing customers is continuously monitored, and, if the payment behavior indicates sufficient risk within the meaning of the applicable utility regulation, customers will be required to provide a security deposit. Investment in Unconsolidated Affiliates The Company's investment in Enable is considered to be a variable interest entity because the owners of the equity at risk in this entity have disproportionate voting rights in relation to their obligations to absorb the entity's expected losses or to receive its expected residual returns. However, the Company is not considered the primary beneficiary of Enable since it does not have the power to direct the activities of Enable that are considered most significant to the economic performance of Enable; therefore, the Company accounts for its investment in Enable using the equity method of accounting. Under the equity method, the investment will be adjusted each period for contributions made, distributions received and the Company's share of the investee's comprehensive income as adjusted for basis differences. The Company's maximum exposure to loss related to Enable is limited to the Company's equity investment in Enable at December 31, 2019 as presented in Note 14. The Company evaluates its equity method investments for impairment when events or changes in circumstances indicate there is a loss in value of the investment that is other than a temporary decline. The Company considers distributions received from Enable which do not exceed cumulative equity in earnings subsequent to the date of investment to be a return on investment and are classified as operating activities in the Consolidated Statements of Cash Flows. The Company considers distributions received from Enable in excess of cumulative equity in earnings subsequent to the date of investment to be a return of investment and are classified as investing activities in the Consolidated Statements of Cash Flows. Allowance for Funds Used During Construction Collection of Sales Tax In the normal course of its operations, OG&E collects sales tax from its customers. OG&E records a current liability for sales taxes when it bills its customers and eliminates this liability when the taxes are remitted to the appropriate governmental authorities. OG&E excludes the sales tax collected from its operating revenues. Revenue Recognition General OG&E recognizes revenue from electric sales when power is delivered to customers. The performance obligation to deliver electricity is generally created and satisfied simultaneously, and the provisions of the regulatory-approved tariff determine the charges OG&E may bill the customer, payment due date and other pertinent rights and obligations of both parties. OG&E reads its customers' meters and sends bills to its customers throughout each month. As a result, there is a significant amount of customers' electricity consumption that has not been billed at the end of each month. OG&E accrues an estimate of the revenues for electric sales delivered since the latest billings. Unbilled revenue is presented in Accrued Unbilled Revenues in the Consolidated Balance Sheets and in Revenues from Contracts with Customers in the Consolidated Statements of Income based on estimates of usage and prices during the period. The estimates that management uses in this calculation could vary from the actual amounts to be paid by customers. Integrated Market and Transmission OG&E currently owns and operates transmission and generation facilities as part of a vertically integrated utility. OG&E is a member of the SPP regional transmission organization and has transferred operational authority, but not ownership, of OG&E's transmission facilities to the SPP. The SPP has implemented FERC-approved regional day-ahead and real-time markets for energy and operating services, as well as associated transmission congestion rights. Collectively the three markets operate together under the global name, SPP Integrated Marketplace. OG&E represents owned and contracted generation assets and customer load in the SPP Integrated Marketplace for the sole benefit of its customers. OG&E has not participated in the SPP Integrated Marketplace for any speculative trading activities. OG&E records the SPP Integrated Marketplace transactions as sales or purchases per FERC Order 668, which requires that purchases and sales be recorded on a net basis for each settlement period of the SPP Integrated Marketplace. Purchases and sales are based on the fixed transaction price determined by the market at the time of the purchase or sale and the MWh quantity purchased or sold. These results are reported as Revenues from Contracts with Customers or Cost of Sales in the Consolidated Financial Statements. OG&E revenues, expenses, assets and liabilities may be adversely affected by changes in the organization, operating and regulation by the FERC or the SPP. OG&E's transmission revenues are generated by the use of OG&E's transmission network by the SPP, which operates the network, on behalf of other transmission owners. OG&E recognizes revenue on the sale of transmission service to its customers over time as the service is provided in the amount OG&E has a right to invoice. Transmission service to the SPP is billed monthly based on a fixed transaction price determined by OG&E's FERC-approved formula transmission rates along with other SPP-specific charges and the megawatt quantity reserved. Other Revenues Revenues from Alternative Revenue Programs Other Revenues in the Consolidated Statements of Income is comprised of certain rider revenue that includes alternative revenue measures as defined in ASC 980, "Regulated Operations," which details two types of alternative revenue programs. The first type adjusts billings for the effects of weather abnormalities or broad external factors or to compensate OG&E for demand-side management initiatives (i.e., no-growth plans and similar conservation efforts). The second type provides for additional billings (i.e., incentive awards) for the achievement of certain objectives, such as reducing costs, reaching specified milestones or demonstratively improving customer service. Once the specific events permitting billing of the additional revenues under either program type have been completed, OG&E recognizes the additional revenues if (i) the program is established by an order from OG&E's regulatory commission that allows for automatic adjustment of future rates; (ii) the amount of additional revenues for the period is objectively determinable and is probable of recovery; and (iii) the additional revenues will be collected within 24 months following the end of the annual period in which they are recognized. Fuel Adjustment Clauses The actual cost of fuel used in electric generation and certain purchased power costs are passed through to OG&E's customers through fuel adjustment clauses. The fuel adjustment clauses are subject to periodic review by the OCC and the APSC. Income Taxes The Company files consolidated income tax returns in the U.S. federal jurisdiction and various state jurisdictions. Income taxes are generally allocated to each company in the affiliated group based on its stand-alone taxable income or loss. Federal investment tax credits previously claimed on electric utility property have been deferred and will be amortized to income over the life of the related property. The Company uses the asset and liability method of accounting for income taxes. Under this method, a deferred tax asset or liability is recognized for the estimated future tax effects attributable to temporary differences between the financial statement basis and the tax basis of assets and liabilities as well as tax credit carry forwards and net operating loss carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period of the change. The Company recognizes interest related to unrecognized tax benefits in Interest Expense and recognizes penalties in Other Expense in the Consolidated Statements of Income. Accrued Vacation The Company accrues vacation pay monthly by establishing a liability for vacation earned. Vacation may be taken as earned and is charged against the liability. At the end of each year, the liability represents the amount of vacation earned but not taken.
Comprehensive Income (Loss) Note [Text Block]	Accumulated Other Comprehensive Income (Loss) The following tables summarize changes in the components of accumulated other comprehensive income (loss) attributable to the Company during 2018 and 2019. All amounts below are presented net of tax. Pension Plan and Restoration of Retirement Income Plan Postretirement Benefit Plans (In millions) Net Gain Net Gain (Loss) Prior Service Cost (Credit) Other Comprehensive Loss from Unconsolidated Affiliates Total Balance at December 31, 2017 $ (32.7) $ 2.5 $ 7.0 $ — $ (23.2) Other comprehensive income (loss) before reclassifications (14.1) 2.1 — — (12.0) Amounts reclassified from accumulated other comprehensive income (loss) 3.3 — (1.7) — 1.6 Settlement cost 4.7 — — — 4.7 Net current period other comprehensive income (loss) (6.1) 2.1 (1.7) — (5.7) Balance at December 31, 2018 (38.8) 4.6 5.3 — (28.9) Other comprehensive income (loss) before reclassifications (8.3) (0.2) — (0.6) (9.1) Amounts reclassified from accumulated other comprehensive income (loss) 3.4 (0.2) (1.7) — 1.5 Settlement cost 8.6 — — — 8.6 Net current period other comprehensive income (loss) 3.7 (0.4) (1.7) (0.6) 1.0 Balance at December 31, 2019 $ (35.1) $ 4.2 $ 3.6 $ (0.6) $ (27.9) The following table summarizes significant amounts reclassified out of accumulated other comprehensive income (loss) by the respective line items in net income during the years ended December 31, 2019 and 2018. Details about Accumulated Other Comprehensive Income (Loss) Components Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Consolidated Statements of Income Year Ended December 31, (In millions) 2019 2018 Amortization of Pension Plan and Restoration of Retirement Income Plan items: Actuarial losses $ (4.5) $ (4.4) (A) Settlement cost (11.3) (6.3) (A) (15.8) (10.7) Income Before Taxes (3.8) (2.7) Income Tax Expense $ (12.0) $ (8.0) Net Income Amortization of postretirement benefit plans items: Prior service credit $ 2.3 $ 2.3 (A) Actuarial gains 0.2 — (A) 2.5 2.3 Income Before Taxes 0.6 0.6 Income Tax Expense $ 1.9 $ 1.7 Net Income Total reclassifications for the period, net of tax $ (10.1) $ (6.3) Net Income (A) These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost (see Note 13 for additional information). The amounts in accumulated other comprehensive loss (gain) at December 31, 2019 that are expected to be recognized into earnings in 2020 are as follows: (In millions) Pension Plan and Restoration of Retirement Income Plan: Net gain $ (4.2) Postretirement Benefit Plans: Net loss 0.2 Prior service cost 2.3 Total, net of tax $ (1.7)
Asset Retirement Obligation Disclosure [Text Block]	OG&E has asset retirement obligations primarily associated with the removal of company-owned wind turbines on leased land, as well as the removal of asbestos from certain power generating stations. The Company has recorded asset retirement obligations that are being accreted over their respective lives ranging from ten to 68 years. The following table summarizes changes to the Company's asset retirement obligations during the years ended December 31, 2019 and 2018. (In millions) 2019 2018 Balance at January 1 $ 83.9 $ 75.1 Accretion expense 1.0 3.4 Revisions in estimated cash flows (A) (2.4) 6.8 Liabilities settled (B) (9.0) (1.4) Balance at December 31 $ 73.5 $ 83.9 (A) Assumptions changed related to the estimated cost of the removal of wind turbine assets and asbestos removal at OG&E's generating facilities. (B) Asset retirement obligations were settled for asbestos removal and for the closure of an ash pond at OG&E's generating facilities.
Property, Plant and Equipment Disclosure [Text Block]	Property, Plant and Equipment All property, plant and equipment is recorded at cost. Newly constructed plant is added to plant balances at cost which includes contracted services, direct labor, materials, overhead, transportation costs and the allowance for funds used during construction. Replacements of units of property are capitalized as plant. For assets that belong to a common plant account, the replaced plant is removed from plant balances, and the cost of such property net of any salvage proceeds is charged to Accumulated Depreciation. For assets that do not belong to a common plant account, the replaced plant is removed from plant balances with the related accumulated depreciation, and the remaining balance net of any salvage proceeds is recorded as a loss in the Consolidated Statements of Income as Other Expense. Repair and replacement of minor items of property are included in the Consolidated Statements of Income as Other Operation and Maintenance Expense. The tables below present OG&E's ownership interest in the jointly-owned McClain Plant and the jointly-owned Redbud Plant, and, as disclosed below, only OG&E's ownership interest is reflected in the property, plant and equipment and accumulated depreciation balances in these tables. The owners of the remaining interests in the McClain Plant and the Redbud Plant are responsible for providing their own financing of capital expenditures. Also, only OG&E's proportionate interests of any direct expenses of the McClain Plant and the Redbud Plant, such as fuel, maintenance expense and other operating expenses, are included in the applicable financial statement captions in the Consolidated Statements of Income. December 31, 2019 (In millions) Percentage Ownership Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment McClain Plant (A) 77 % $ 254.4 $ 83.5 $ 170.9 Redbud Plant (A)(B) 51 % $ 529.9 $ 159.0 $ 370.9 (A) Construction work in progress was $0.2 million and $1.4 million for the McClain and Redbud Plants, respectively. (B) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million. December 31, 2018 (In millions) Percentage Ownership Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment McClain Plant (A) 77 % $ 227.2 $ 78.2 $ 149.0 Redbud Plant (A)(B) 51 % $ 493.9 $ 145.3 $ 348.6 (A) Construction work in progress was $0.2 million and $0.9 million for the McClain and Redbud Plants, respectively. (B) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million. The Company's property, plant and equipment and related accumulated depreciation are divided into the following major classes: December 31, 2019 (In millions) Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment OGE Energy: Property, plant and equipment $ 6.1 $ — $ 6.1 OGE Energy property, plant and equipment 6.1 — 6.1 OG&E: Distribution assets 4,468.6 1,381.1 3,087.5 Electric generation assets (A) 4,838.6 1,601.0 3,237.6 Transmission assets (B) 2,901.1 565.5 2,335.6 Intangible plant 225.2 145.4 79.8 Other property and equipment 473.1 175.1 298.0 OG&E property, plant and equipment 12,906.6 3,868.1 9,038.5 Total property, plant and equipment $ 12,912.7 $ 3,868.1 $ 9,044.6 (A) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million. (B) This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.8 million. December 31, 2018 (In millions) Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment OGE Energy: Property, plant and equipment $ 6.1 $ — $ 6.1 OGE Energy property, plant and equipment 6.1 — 6.1 OG&E: Distribution assets 4,229.4 1,324.5 2,904.9 Electric generation assets (A) 4,657.2 1,572.8 3,084.4 Transmission assets (B) 2,846.7 534.2 2,312.5 Intangible plant 187.6 135.1 52.5 Other property and equipment 444.2 160.8 283.4 OG&E property, plant and equipment 12,365.1 3,727.4 8,637.7 Total property, plant and equipment $ 12,371.2 $ 3,727.4 $ 8,643.8 (A) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million. (B) This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.7 million. OG&E's unamortized computer software costs, included in intangible plant above, were $71.3 million and $44.3 million at December 31, 2019 and 2018, respectively. The following table summarizes the Company's amortization expense for computer software costs. Year Ended December 31 (In millions) 2019 2018 2017 OGE Energy $ — $ — $ 0.2 OG&E 11.0 9.6 8.8 Total $ 11.0 $ 9.6 $ 9.0 Depreciation and Amortization The provision for depreciation, which was 2.7 percent of the average depreciable utility plant for both 2019 and 2018, is calculated using the straight-line method over the estimated service life of the utility assets. Depreciation is provided at the unit level for production plant and at the account or sub-account level for all other plant and is based on the average life group method. In 2020, the provision for depreciation is projected to be 2.7 percent of the average depreciable utility plant. Amortization of intangible assets is calculated using the straight-line method. Of the remaining amortizable intangible plant balance at December 31, 2019, 98.9 percent will be amortized over 10.4 years with the remaining 1.1 percent of the intangible plant balance at December 31, 2019 being amortized over 23.7 years. Amortization of plant acquisition adjustments is provided on a straight-line basis over the estimated remaining service life of the acquired assets. Plant acquisition adjustments include $148.3 million for the Redbud Plant, which is being amortized over a 27 year life and $3.3 million for certain transmission substation facilities in OG&E's service territory, which are being amortized over a 37 to 59 year period.
Inventory Disclosure [Text Block]	Fuel Inventories Fuel inventories for the generation of electricity consist of coal, natural gas and oil. OG&E uses the weighted-average cost method of accounting for inventory that is physically added to or withdrawn from storage or stockpiles. The amount of fuel inventory was $46.3 million and $57.6 million at December 31, 2019 and 2018, respectively.
Summary of Significant Accounting Policies [Text Block]	Accounting Records The accounting records of OG&E are maintained in accordance with the Uniform System of Accounts prescribed by the FERC and adopted by the OCC and the APSC. Additionally, OG&E, as a regulated utility, is subject to accounting principles for certain types of rate-regulated activities, which provide that certain incurred costs that would otherwise be charged to expense can be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense can be deferred as regulatory liabilities, based on the expected flowback to customers in future rates. Management's expected recovery of deferred costs and flowback of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. OG&E records certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refund in future rates. The following table is a summary of OG&E's regulatory assets and liabilities. December 31 (In millions) 2019 2018 REGULATORY ASSETS Current: Fuel clause under recoveries $ 39.5 $ 2.0 Production tax credit rider over credit (A) 1.7 6.9 Oklahoma demand program rider under recovery (A) — 6.4 Other (A) 7.5 3.2 Total current regulatory assets $ 48.7 $ 18.5 Non-current: Benefit obligations regulatory asset $ 167.2 $ 188.2 Deferred storm expenses 65.5 36.5 Sooner Dry Scrubbers 20.6 4.5 Smart Grid 18.4 25.6 Unamortized loss on reacquired debt 10.6 11.4 Arkansas deferred pension expenses 8.0 6.8 Pension tracker 2.3 — Other 13.4 12.8 Total non-current regulatory assets $ 306.0 $ 285.8 REGULATORY LIABILITIES Current: Reserve for tax refund and interim surcharge (B) $ 12.7 $ 15.4 Fuel clause over recoveries 4.8 0.3 SPP cost tracker over recovery (B) 2.6 16.8 Oklahoma demand program rider over recovery (B) 2.0 — Transmission cost recovery rider over recovery (B) — 2.7 Other (B) 6.9 1.4 Total current regulatory liabilities $ 29.0 $ 36.6 Non-current: Income taxes refundable to customers, net $ 899.2 $ 937.1 Accrued removal obligations, net 318.5 308.1 Pension tracker — 18.7 Other 5.8 6.8 Total non-current regulatory liabilities $ 1,223.5 $ 1,270.7 (A) Included in Other Current Assets in the Consolidated Balance Sheets. (B) Included in Other Current Liabilities in the Consolidated Balance Sheets. Fuel clause under and over recoveries are generated from OG&E's customers when OG&E's cost of fuel either exceeds or is less than the amount billed to its customers, respectively. OG&E's fuel recovery clauses are designed to smooth the impact of fuel price volatility on customers' bills. As a result, OG&E under recovers fuel costs in periods of rising fuel prices above the baseline charge for fuel and over recovers fuel costs when prices decline below the baseline charge for fuel. Provisions in the fuel clauses are intended to allow OG&E to amortize under and over recovery balances. As approved by the OCC, OG&E utilizes a rider separate from base rates to credit customers for production tax credits. OG&E recovers program costs related to the Demand and Energy Efficiency Program in Oklahoma through the Demand Program Rider, which operates on a three-year program cycle. The current program cycle, which runs through 2021, includes recovery of (i) energy efficiency program costs, (ii) lost revenues associated with certain achieved energy efficiency and demand savings, (iii) performance-based incentives and (iv) costs associated with research and development investments. The benefit obligations regulatory asset is comprised of expenses recorded which are probable of future recovery and that have not yet been recognized as components of net periodic benefit cost, including net loss and prior service cost. These expenses are recorded as a regulatory asset as OG&E historically has recovered and currently recovers pension and postretirement benefit plan expense in its electric rates. If, in the future, the regulatory bodies indicate a change in policy related to the recovery of pension and postretirement benefit plan expenses, this could cause the benefit obligations regulatory asset balance to be reclassified to accumulated other comprehensive income. The following table is a summary of the components of the benefit obligations regulatory asset: December 31 (In millions) 2019 2018 Pension Plan and Restoration of Retirement Income Plan: Net loss $ 160.5 $ 185.3 Postretirement Benefit Plans: Net loss 23.3 25.6 Prior service cost (16.6) (22.7) Total $ 167.2 $ 188.2 The following amounts in the benefit obligations regulatory asset at December 31, 2019 are expected to be recognized as components of net periodic benefit cost in 2020: (In millions) Pension Plan and Restoration of Retirement Income Plan: Net loss $ 11.4 Postretirement Benefit Plans: Net loss 2.8 Prior service cost (6.1) Total $ 8.1 OG&E includes in expense any Oklahoma storm-related operation and maintenance expenses up to $2.7 million annually and defers to a regulatory asset any additional expenses incurred over $2.7 million. OG&E expects to recover the amounts deferred each year over a five-year period in accordance with historical practice. As approved by the OCC in June 2018, OG&E deferred the non-fuel incremental operation and maintenance expenses, depreciation, debt cost associated with the capital investment and related ad valorem taxes for the Dry Scrubbers at Sooner Units 1 and 2 as a regulatory asset. As approved by the OCC, these costs are being recovered over 25 years. OG&E deferred to a regulatory asset the incremental and stranded costs that were accumulated during Smart Grid deployment, including (i) costs for web portal access, (ii) costs for education and home energy reports and (iii) stranded costs associated with OG&E's analog electric meters, which have been replaced by smart meters. As approved by the OCC and APSC, these costs are being recovered over a six-year period. Unamortized loss on reacquired debt is comprised of unamortized debt issuance costs related to the early retirement of OG&E's long-term debt. These amounts are recorded in interest expense and are being amortized over the term of the long-term debt which replaced the previous long-term debt. The unamortized loss on reacquired debt is recovered as a part of OG&E's cost of capital. Arkansas includes a certain level of pension expense in base rates. When the Pension Plan experiences a settlement, which represents an acceleration of future pension costs, OG&E defers to a regulatory asset the Arkansas jurisdictional portion of each settlement, which historically was recovered from customers over the average life of the remaining plan participants. A portion of these settlements is being recovered in current rates, and recovery of additional amounts will be requested as additional settlements occur. For additional information related to settlements, see Note 13. OG&E recovers specific amounts of pension and postretirement medical costs in rates approved in its Oklahoma rate reviews. In accordance with approved orders, OG&E defers the difference between actual pension and postretirement medical expenses and the amount approved in its last Oklahoma rate review as a regulatory asset or regulatory liability. These amounts have been recorded in the Pension tracker regulatory asset in the table above. As a result of 2018 filings with the OCC, APSC and FERC, OG&E established mechanisms to refund to customers the amount of excess taxes received through rates, with an ongoing adjustment for any excess accumulated deferred income taxes resulting from the 2017 Tax Act. Additional amounts due to customers will be refunded in accordance with agreements in each jurisdiction. OG&E recovers certain SPP costs related to base plan charges from its customers and refunds certain SPP revenues received to its customers in Oklahoma through the SPP cost tracker and in Arkansas through the transmission cost recovery rider. Income taxes refundable to customers, net, represents the reduction in accumulated deferred income taxes resulting from the reduction in the federal income tax rate as part of the 2017 Tax Act and includes income taxes recoverable from customers that represent income tax benefits previously used to reduce OG&E's revenues (treated as regulatory assets). These liabilities will be returned to customers in varying amounts over approximately 80 years, and the assets will be amortized over the estimated remaining life of the assets to which they relate, as the temporary differences that generated the income tax benefits turn around.
Reclassifications [Text Block]	ReclassificationsCertain prior year amounts have been reclassified to conform to the current year presentation.

Accounting Pronouncements

Accounting Pronouncements	12 Months Ended
	Dec. 31, 2019
Accounting Pronouncement [Abstract]
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]	Accounting Pronouncements Recently Adopted Accounting Standards Leases. In February 2016, the FASB issued ASU 2016-02, "Leases (Topic 842)." The main difference between prior lease accounting and ASC 842 is the recognition of right-of-use assets and lease liabilities by lessees for those leases classified as operating leases under current accounting guidance. Lessees, such as the Company, recognize a right-of-use asset and a lease liability for virtually all of their leases, other than leases that meet the definition of a short-term lease. The liability is equal to the present value of lease payments. The asset is based on the liability, subject to adjustment for items such as initial direct costs. For income statement purposes, ASC 842 retains a dual model, requiring leases to be classified as either operating or finance. Operating leases result in straight-line expense, while finance leases result in a front-loaded expense pattern, similar to prior capital leases. Classification of operating and finance leases is based on criteria that are largely similar to those applied in prior lease guidance but without the explicit thresholds. The Company adopted this standard in the first quarter of 2019 utilizing the modified retrospective transition method. Various practical expedients for the application of ASC 842 were approved, and the Company elected to apply the below: • a package of practical expedients allowing entities to not reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) initial direct costs for any existing leases; • an option that permits an entity to elect a transitional practical expedient, to be applied consistently, to not evaluate under ASC 842 land easements that exist or expired before the entity's adoption of ASC 842 and that were not previously accounted for as leases under ASC 840, "Leases"; and • an option that permits an entity to elect to initially apply ASC 842 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption, provided that if an entity elects this additional (and optional) transition method, the entity will provide the required ASC 840 disclosures for all periods that continue to be reported under ASC 840. The Company evaluated its current lease contracts and, at January 1, 2019, recognized $34.5 million and $39.1 million of operating lease right-of-use assets and liabilities, respectively, for railcar, wind farm land and office space leases in the Consolidated Balance Sheet. The new standard did not have a material impact on the Company's 2019 Consolidated Statement of Income. Further, the Company evaluated its existing processes and controls regarding lease identification, accounting and presentation and implemented changes as necessary in order to adequately address the requirements of ASC 842. Financial Instruments-Credit Losses. In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Information." The amendments in this update require entities to measure all expected credit losses of financial assets held at a reporting date based on historical experience, current conditions and reasonable and supportable forecasts in order to record credit losses in a more timely manner. ASU 2016-13 also amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. ASU 2016-13 is effective for fiscal years beginning after December 2019 and is applied utilizing a modified-retrospective approach. The Company determined the only financial instrument that the Company currently holds and is required to measure under ASU 2016-13 is its trade receivables. Upon adoption of this ASU, the Company considers forecasts of future economic conditions in addition to the historical data utilized prior to ASU 2016-13 when measuring the reserve for trade receivables. The Company evaluated its reserve for trade receivables in light of the new guidance and determined that no adjustment was necessary to the amount recorded as of January 1, 2020. Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. In August 2018, the FASB issued ASU 2018-15, "Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract." The new guidance aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ASU 2018-15 is effective for fiscal years beginning after December 2019 and can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company adopted and prospectively applied the new guidance beginning in the first quarter of 2020, which did not have a material effect on the Consolidated Financial Statements upon adoption. Issued Accounting Standards Not Yet Adopted Simplifying the Accounting for Income Taxes. In December 2019, the FASB issued ASU 2019-12, "Income Taxes (Topic 740)." The new guidance simplifies the accounting for income taxes by removing certain exceptions to the general principles in ASC 740 and improves consistent application of existing guidance. ASU 2019-12 will be effective for the Company as of January 1, 2021 and can be early adopted. The Company is currently assessing the impact of these rule changes on its Consolidated Financial Statements. Investments - Equity Method and Joint Ventures. In January 2020, the FASB issued ASU 2020-01, "Investments - Equity Securities (Topic 321), Investments - Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815)." The new guidance makes targeted improvements to address certain aspects of accounting for financial instruments, clarifying the interaction of the accounting for equity securities under ASC 321 and investments accounted for under the equity method of accounting in ASC 323. ASU 2020-01 should be applied prospectively and will be effective for the

Revenue from Contracts with Cus

Revenue from Contracts with Customers (Notes)	9 Months Ended
	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue Recognition The following table disaggregates the Company's revenues from contracts with customers by customer classification. The Company's operating revenues disaggregated by customer classification can be found in "OG&E (Electric Utility) Results of Operations" within "Item 7. Management's Discussion and Analysis of Financial Condition and Results of Operations." Year Ended December 31, (In millions) 2019 2018 Residential $ 865.8 $ 877.8 Commercial 486.6 500.0 Industrial 217.8 228.9 Oilfield 200.4 190.4 Public authorities and street light 190.3 197.4 System sales revenues 1,960.9 1,994.5 Provision for rate refund (0.9) (6.0) Integrated market 38.4 48.7 Transmission 148.0 147.4 Other 29.1 27.1 Revenues from contracts with customers $ 2,175.5 $ 2,211.7

Leases, Codification Topic 842

Leases, Codification Topic 842	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases of Lessee Disclosure	Leases Based on its evaluation of all contracts under ASC 842, as described in Note 1, the Company concluded it has operating lease obligations for OG&E railcar leases, OG&E wind farm land leases and the Company's office space lease. Operating Leases OG&E Railcar Lease Agreement Effective February 1, 2019, OG&E renewed a railcar lease agreement for 780 rotary gondola railcars to transport coal from Wyoming to OG&E's coal-fired generation units. Rental payments are charged to fuel expense and are recovered through OG&E's fuel adjustment clauses. On February 1, 2024, OG&E has the option to either purchase the railcars at a stipulated fair market value or renew the lease. If OG&E chooses not to purchase the railcars or renew the lease agreement and the actual fair value of the railcars is less than the stipulated fair market value, OG&E would be responsible for the difference in those values up to a maximum of $6.8 million. OG&E Wind Farm Land Lease Agreements OG&E has operating leases related to land for OG&E's Centennial, OU Spirit and Crossroads wind farms with terms of 25 to 30 years. The Centennial lease has rent escalations which increase annually based on the Consumer Price Index. While lease liabilities are not remeasured as a result of changes to the Consumer Price Index, changes to the Consumer Price Index are treated as variable lease payments and recognized in the period in which the obligation for those payments was incurred. The OU Spirit and Crossroads leases have rent escalations which increase after five and 10 years. Although the leases are cancellable, OG&E is required to make annual lease payments as long as the wind turbines are located on the land. OG&E does not expect to terminate the leases until the wind turbines reach the end of their useful life. Office Space Lease The Company has a noncancellable office space lease agreement, with a term from September 1, 2018 to August 31, 2021, that allows for leasehold improvements. Financial Statement Information and Maturity Analysis of Lease Liabilities Operating lease cost was $6.0 million, $4.9 million and $6.2 million for the years ended December 31, 2019, 2018 and 2017, respectively. The following table presents amounts recognized for operating leases in the Company's 2019 Consolidated Cash Flow Statement and Balance Sheet and supplemental information related to those amounts recognized, as well as a maturity analysis of the Company's operating lease liabilities. (In millions) Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 5.6 Right-of-use assets obtained in exchange for new operating lease liabilities $ 10.7 (Dollars in millions) December 31, 2019 Right-of-use assets at period end (A) $ 40.9 Operating lease liabilities at period end (B) $ 45.8 Operating lease weighted-average remaining lease term (in years) 13.1 Operating lease weighted-average discount rate 3.9 % December 31, Future minimum operating lease payments as of: 2019 2018(C)(D) (In millions) 2019 $ — $ 22.1 2020 6.2 3.9 2021 5.8 3.5 2022 5.2 2.9 2023 5.2 2.9 2024 3.1 3.0 Thereafter 34.7 34.6 Total future minimum lease payments 60.2 $ 72.9 Less: Imputed interest 14.4 Present value of net minimum lease payments $ 45.8 (A) Included in Property, Plant and Equipment in the 2019 Consolidated Balance Sheet. (B) Included in Other Deferred Credits and Other Liabilities in the 2019 Consolidated Balance Sheet. (C) Amounts included for comparability and accounted for in accordance with ASC 840, "Leases." (D) At the end of the railcar lease term, which was February 1, 2019, OG&E had the option to either purchase the railcars at a stipulated fair market value or renew the lease. OG&E renewed the lease effective February 1, 2019. If OG&E chose not to purchase the railcars or renew the lease agreement and the actual fair value of the railcars was less than the stipulated fair market value, OG&E would have been responsible for the difference in those values up to a maximum of $16.2 million.

Investment in Unconsolidated Af

Investment in Unconsolidated Affiliate and Related Party Transactions	12 Months Ended
	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Equity Method Investments and Joint Ventures Disclosure [Text Block]	Investment in Unconsolidated Affiliates and Related Party Transactions In 2013, the Company, CenterPoint and the ArcLight group formed Enable as a private limited partnership, and the Company and the ArcLight group indirectly contributed 100 percent of the equity interests in Enogex LLC to Enable. The Company determined that its contribution of Enogex LLC to Enable met the requirements of being in substance real estate and recorded the contribution at historical cost. The formation of Enable was considered a business combination, and CenterPoint was the acquirer of Enogex Holdings for accounting purposes. Under this method, the fair value of the consideration paid by CenterPoint for Enogex Holdings was allocated to the assets acquired and liabilities assumed based on their fair value. Enogex Holdings' assets, liabilities and equity were accordingly adjusted to estimated fair value, resulting in an increase to Enable's equity of $2.2 billion. Since the contribution of Enogex LLC to Enable was recorded at historical cost, the effects of the amortization and depreciation expense associated with the fair value adjustments on Enable's results of operations have been eliminated in the Company's recording of its equity in earnings of Enable. As prior real estate sales accounting guidance was superseded by ASU 2017-05, "Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets," the Company recognizes gains or losses on sales or dilution events in the Company's investment in Enable within the Company's earnings, net of proportional basis difference recognition. At December 31, 2019, the Company owned 111.0 million common units, or 25.5 percent, of Enable's outstanding common units. On December 31, 2019, Enable's common unit price closed at $10.03. The Company recorded equity in earnings of unconsolidated affiliates of $113.9 million, $152.8 million and $131.2 million for the years ended December 31, 2019, 2018 and 2017, respectively. Equity in earnings of unconsolidated affiliates includes the Company's share of Enable's earnings adjusted for the amortization of the basis difference of the Company's original investment in Enogex LLC and its underlying equity in the net assets of Enable. The basis difference is being amortized, beginning in 2013, over the average life of the assets to which the basis difference is attributed, which is approximately 30 years. Equity in earnings of unconsolidated affiliates is also adjusted for the elimination of the Enogex Holdings fair value adjustments, as described above. These amortizations may also include gain or loss on dilution, net of proportional basis difference recognition. Summarized unaudited financial information for 100 percent of Enable is presented below as of December 31, 2019 and 2018 and for the years ended December 31, 2019, 2018 and 2017. December 31, Balance Sheet 2019 2018 (In millions) Current assets $ 389 $ 449 Non-current assets $ 11,877 $ 11,995 Current liabilities $ 780 $ 1,615 Non-current liabilities $ 4,077 $ 3,211 Year Ended December 31, Income Statement 2019 2018 2017 (In millions) Total revenues $ 2,960 $ 3,431 $ 2,803 Cost of natural gas and NGLs $ 1,279 $ 1,819 $ 1,381 Operating income $ 569 $ 648 $ 528 Net income $ 360 $ 485 $ 400 The following table reconciles OGE Energy's equity in earnings of unconsolidated affiliates for the years ended December 31, 2019, 2018 and 2017. Year Ended December 31, (In millions) 2019 2018 2017 Enable net income $ 360.0 $ 485.3 $ 400.3 OGE Energy's percent ownership at period end 25.5 % 25.6 % 25.7 % OGE Energy's portion of Enable net income $ 91.8 $ 124.4 $ 102.7 Amortization of basis difference and dilution recognition (A) 22.1 28.4 28.5 Equity in earnings of unconsolidated affiliates $ 113.9 $ 152.8 $ 131.2 (A) Includes loss on dilution, net of proportional basis difference recognition. The following table reconciles the difference between OGE Energy's investment in Enable and its underlying equity in the net assets of Enable (basis difference) from December 31, 2018 to December 31, 2019. (In millions) Basis difference at December 31, 2018 $ 680.3 Amortization of basis difference (A) (27.8) Basis difference at December 31, 2019 $ 652.5 (A) Includes proportional basis difference recognition due to dilution. On February 7, 2020, Enable announced a quarterly dividend distribution of $0.33050 per unit on its outstanding common units, which is unchanged from the previous quarter. If cash distributions to Enable's unitholders exceed $0.330625 per unit in any quarter, the general partner will receive increasing percentages, up to 50 percent, of the cash Enable distributes in excess of that amount. The Company is entitled to 60 percent of those "incentive distributions." In certain circumstances, the general partner has the right to reset the minimum quarterly distribution and the target distribution levels at which the incentive distributions receive increasing percentages to higher levels based on Enable's cash distributions at the time of the exercise of this reset election. Distributions received from Enable were $144.0 million, $141.2 million and $141.2 million during the years ended December 31, 2019, 2018 and 2017, respectively. Related Party Transactions The Company charges operating costs to OG&E and Enable based on several factors, and operating costs directly related to OG&E and/or Enable are assigned as such. Operating costs incurred for the benefit of OG&E are allocated either as overhead based primarily on labor costs or using the "Distrigas" method, which is a three-factor formula that uses an equal weighting of payroll, net operating revenues and gross property, plant and equipment. The Company and Enable The Company and Enable are currently parties to several agreements whereby the Company provides specified support services to Enable, such as certain information technology, payroll and benefits administration. Under these agreements, the Company charged operating costs to Enable of $0.5 million, $0.6 million and $2.3 million for December 31, 2019, 2018 and 2017, respectively. Pursuant to a seconding agreement, the Company provides seconded employees to Enable to support Enable's operations. As of December 31, 2019, 80 employees that participate in the Company's defined benefit and retirement plans are seconded to Enable. The Company billed Enable for reimbursement of $23.2 million, $27.5 million and $29.5 million in 2019, 2018 and 2017, respectively, under the seconding agreement for employment costs. If the seconding agreement was terminated, and those employees were no longer employed by the Company, and lump sum payments were made to those employees, the Company would recognize a settlement or curtailment of the pension/retiree health care charges, which would increase expense at the Company by $17.3 million. Settlement and curtailment charges associated with the Enable seconded employees are not reimbursable to the Company by Enable. The seconding agreement can be terminated by mutual agreement of the Company and Enable or solely by the Company upon 120 days' notice. The Company had accounts receivable from Enable for amounts billed for support services, including the cost of seconded employees, of $0.8 million and $1.7 million as of December 31, 2019 and 2018, which are included in Accounts Receivable in the Company's Consolidated Balance Sheets. OG&E and Enable Enable provides gas transportation services to OG&E pursuant to an agreement, which expires in May 2024, that grants Enable the responsibility of delivering natural gas to OG&E's generating facilities and performing an imbalance service. With this imbalance service, in accordance with the cash-out provision of the contract, OG&E purchases gas from Enable when Enable's deliveries exceed OG&E's pipeline receipts. Enable purchases gas from OG&E when OG&E's pipeline receipts exceed Enable's deliveries. Further, an additional gas transportation services contract with Enable became effective in December 2018 related to the project to convert Muskogee Units 4 and 5 from coal to natural gas. The following table summarizes related party transactions between OG&E and Enable during the years ended December 31, 2019, 2018 and 2017. Year Ended December 31, (In millions) 2019 2018 2017 Operating revenues: Electricity to power electric compression assets $ 15.9 $ 16.3 $ 14.0 Cost of sales: Natural gas transportation services $ 41.2 $ 37.9 $ 35.0 Natural gas (sales) purchases $ (6.0) $ (3.2) $ (2.1)

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The classification of the Company's fair value measurements requires judgment regarding the degree to which market data is observable or corroborated by observable market data. GAAP establishes a fair value hierarchy that prioritizes the inputs used to measure fair value based on observable and unobservable data. The hierarchy categorizes the inputs into three levels, with the highest priority given to quoted prices in active markets for identical unrestricted assets or liabilities (Level 1) and the lowest priority given to unobservable inputs (Level 3). Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The three levels defined in the fair value hierarchy are as follows: Level 1 inputs are quoted prices in active markets for identical unrestricted assets or liabilities that are accessible at the measurement date. Level 2 inputs are inputs other than quoted prices in active markets included within Level 1 that are either directly or indirectly observable at the reporting date for the asset or liability for substantially the full term of the asset or liability. Level 2 inputs include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. Level 3 inputs are prices or valuation techniques for the asset or liability that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). Unobservable inputs reflect the reporting entity's own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk). The Company had no financial instruments measured at fair value on a recurring basis at December 31, 2019 and 2018. The following table summarizes the carrying amount and fair value of the Company's financial instruments at December 31, 2019 and 2018, as well as the classification level within the fair value hierarchy. 2019 2018 December 31 (In millions) Carrying Amount Fair Carrying Amount Fair Classification Long-term Debt (including Long-term Debt due within one year): OG&E Senior Notes $ 3,050.3 $ 3,500.4 $ 3,001.9 $ 3,178.2 Level 2 OG&E Industrial Authority Bonds $ 135.4 $ 135.4 $ 135.4 $ 135.4 Level 2 Tinker Debt $ 9.5 $ 10.0 $ 9.6 $ 8.7 Level 3

Stock Based Compensation

Stock Based Compensation	12 Months Ended
	Dec. 31, 2019
Stock-Based Compensation [Abstract]
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]	Stock-Based Compensation In 2013, the Company adopted, and its shareholders approved, the Stock Incentive Plan. Under the Stock Incentive Plan, restricted stock, restricted stock units, stock options, stock appreciation rights and performance units may be granted to officers, directors and other key employees of the Company and its subsidiaries. The Company has authorized the issuance of up to 7,400,000 shares under the Stock Incentive Plan. The following table summarizes the Company's pre-tax compensation expense and related income tax benefit for the years ended December 31, 2019, 2018 and 2017 related to the Company's performance units and restricted stock units. Year Ended December 31 (In millions) 2019 2018 2017 Performance units: Total shareholder return $ 8.7 $ 8.2 $ 7.6 Earnings per share 4.3 5.1 1.4 Total performance units 13.0 13.3 9.0 Restricted stock units 0.9 0.1 0.1 Total compensation expense $ 13.9 $ 13.4 $ 9.1 Income tax benefit $ 3.6 $ 3.4 $ 3.5 The Company has issued new shares of common stock to satisfy restricted stock unit grants and payouts of earned performance units. In 2019, 2018 and 2017, there were 443,900 shares, 26,211 shares and 2,298 shares, respectively, of new common stock issued pursuant to the Company's Stock Incentive Plan related to restricted stock unit grants and payouts of earned performance units. Performance Units Under the Stock Incentive Plan, the Company has issued performance units which represent the value of one share of the Company's common stock. The performance units provide for accelerated vesting if there is a change in control (as defined in the Stock Incentive Plan). Each performance unit is subject to forfeiture if the recipient terminates employment with the Company or a subsidiary prior to the end of the primarily three-year award cycle for any reason other than death, disability or retirement. In the event of death, disability or retirement, a participant will receive a prorated payment based on such participant's number of full months of service during the award cycle, further adjusted based on the achievement of the performance goals during the award cycle. The Company estimates expected forfeitures in accounting for performance unit compensation expense. The performance units granted based on total shareholder return are contingently awarded and will be payable in shares of the Company's common stock subject to the condition that the number of performance units, if any, earned by the employees upon the expiration of a primarily three-year award cycle (i.e., three-year cliff vesting period) is dependent on the Company's total shareholder return ranking relative to a peer group of companies. The performance units granted based on earnings per share are contingently awarded and will be payable in shares of the Company's common stock based on the Company's earnings per share growth over a primarily three-year award cycle (i.e., three-year cliff vesting period) compared to a target set at the time of the grant by the Compensation Committee of the Company's Board of Directors. All of these performance units are classified as equity in the Consolidated Balance Sheets. If there is no or only a partial payout for the performance units at the end of the award cycle, the unearned performance units are cancelled. Payout requires approval of the Compensation Committee of the Company's Board of Directors. Payouts, if any, are all made in common stock and are considered made when the payout is approved by the Compensation Committee. Performance Units – Total Shareholder Return The fair value of the performance units based on total shareholder return was estimated on the grant date using a lattice-based valuation model that factors in information, including the expected dividend yield, expected price volatility, risk-free interest rate and the probable outcome of the market condition, over the expected life of the performance units. Compensation expense for the performance units is a fixed amount determined at the grant date fair value and is recognized over the primarily three-year award cycle regardless of whether performance units are awarded at the end of the award cycle. Dividends are accrued on a quarterly basis pending achievement of payout criteria and are included in the fair value calculations. Expected price volatility is based on the historical volatility of the Company's common stock for the past three years and was simulated using the Geometric Brownian Motion process. The risk-free interest rate for the performance unit grants is based on the three-year U.S. Treasury yield curve in effect at the time of the grant. The expected life of the units is based on the non-vested period since inception of the award cycle. There are no post-vesting restrictions related to the Company's performance units based on total shareholder return. The number of performance units granted based on total shareholder return and the assumptions used to calculate the grant date fair value of the performance units based on total shareholder return are shown in the following table. 2019 2018 2017 Number of units granted 208,647 261,916 260,570 Fair value of units granted $ 47.00 $ 36.86 $ 41.77 Expected dividend yield 4.0 % 3.6 % 3.8 % Expected price volatility 17.0 % 19.0 % 19.9 % Risk-free interest rate 2.47 % 2.38 % 1.44 % Expected life of units (in years) 2.86 2.86 2.80 Performance Units – Earnings Per Share The fair value of the performance units based on earnings per share is based on grant date fair value which is equivalent to the price of one share of the Company's common stock on the date of grant. The fair value of performance units based on earnings per share varies as the number of performance units that will vest is based on the grant date fair value of the units and the probable outcome of the performance condition. The Company reassesses at each reporting date whether achievement of the performance condition is probable and accrues compensation expense if and when achievement of the performance condition is probable. As a result, the compensation expense recognized for these performance units can vary from period to period. There are no post-vesting restrictions related to the Company's performance units based on earnings per share. In 2019, the Compensation Committee of the Company's Board of Directors voted to grant restricted stock units in lieu of performance units based on earnings per share. For 2018 and 2017, the number of performance units granted based on earnings per share and the grant date fair value are shown in the following table. 2018 2017 Number of units granted 87,308 86,857 Fair value of units granted $ 31.03 $ 34.83 Restricted Stock Units Under the Stock Incentive Plan, the Company has issued restricted stock units to certain existing non-officer employees as well as other executives upon hire to attract and retain individuals to be competitive in the marketplace, and for the 2019 grant cycle, restricted stock units were granted in lieu of performance units based on earnings per share. The restricted stock units vest primarily in a three-year award cycle (i.e., three-year cliff vesting period). Prior to vesting, each restricted stock unit is subject to forfeiture if the recipient ceases to render substantial services to the Company or a subsidiary. These restricted stock units may not be sold, assigned, transferred or pledged and are subject to a risk of forfeiture. The fair value of the restricted stock units was based on the closing market price of the Company's common stock on the grant date. Compensation expense for the restricted stock units is a fixed amount determined at the grant date fair value and is recognized as services are rendered by employees over a primarily three-year vesting period. Also, for those restricted stock units that vest in one-third annual increments over a three-year cycle, the Company treats its restricted stock units as multiple separate awards by recording compensation expense separately for each tranche whereby a substantial portion of the expense is recognized in the earlier years in the requisite service period. Dividends will only be paid on restricted stock unit awards that vest; therefore, only the present value of dividends expected to vest are included in the fair value calculations. The expected life of the restricted stock units is based on the non-vested period since inception of the primarily three-year award cycle. There are no post-vesting restrictions related to the Company's restricted stock units. The number of restricted stock units granted and the grant date fair value are shown in the following table. 2019 2018 2017 Restricted stock units granted 75,929 826 3,145 Fair value of restricted stock units granted $ 41.71 $ 36.28 $ 34.96 Performance Units and Restricted Stock Units Activity A summary of the activity for the Company's performance units and restricted stock units at December 31, 2019 and changes in 2019 are shown in the following table. Performance Units Restricted Total Shareholder Return Earnings Per Share (Dollars in millions) Number Aggregate Intrinsic Value Number Aggregate Intrinsic Value Number Aggregate Intrinsic Value Units/shares outstanding at 12/31/18 755,480 251,825 2,711 Granted 208,647 (A) — 75,929 Converted (274,078) (B) $ 19.8 (91,356) (B) $ 7.2 N/A Vested N/A N/A (2,161) $ 0.1 Forfeited (25,232) (5,298) (3,599) Units/shares outstanding at 12/31/19 664,817 $ 35.4 155,171 $ 11.5 72,880 $ 3.2 Units/shares fully vested at 12/31/19 222,163 $ 11.5 74,053 $ 6.6 (A) For performance units, this represents the target number of performance units granted. Actual number of performance units earned, if any, is dependent upon performance and may range from zero percent to 200 percent of the target. (B) These amounts represent performance units that vested at December 31, 2018 which were settled in February 2019. A summary of the activity for the Company's non-vested performance units and restricted stock units at December 31, 2019 and changes in 2019 are shown in the following table. Performance Units Restricted Total Shareholder Return Earnings Per Share Number Weighted-Average Number Weighted-Average Number Weighted-Average Units/shares non-vested at 12/31/18 481,402 $ 39.17 160,469 $ 32.82 2,711 $ 35.00 Granted 208,647 (A) $ 47.00 — $ — 75,929 $ 41.71 Vested (222,163) $ 41.76 (74,053) $ 34.83 (2,161) $ 34.66 Forfeited (25,232) $ 41.45 (5,298) $ 32.07 (3,599) $ 41.78 Units/shares non-vested at 12/31/19 442,654 $ 41.43 81,118 $ 31.03 72,880 $ 41.66 Units/shares expected to vest 418,331 (B) 77,617 (B) 54,102 (B) (A) For performance units, this represents the target number of performance units granted. Actual number of performance units earned, if any, is dependent upon performance and may range from zero percent to 200 percent of the target. (B) The intrinsic value of the performance units based on total shareholder return and earnings per share is $22.8 million and $4.7 million, respectively. The intrinsic value of restricted stock units is $2.4 million. Fair Value of Vested Performance Units and Restricted Stock Units A summary of the Company's fair value for its vested performance units and restricted stock units is shown in the following table. Year Ended December 31 (In millions) 2019 2018 2017 Performance units: Total shareholder return $ 9.3 $ 5.9 $ 6.3 Earnings per share $ 5.2 $ 4.9 $ 1.2 Restricted stock units $ 0.1 $ 0.1 $ 0.1 Unrecognized Compensation Cost A summary of the Company's unrecognized compensation cost for its non-vested performance units and restricted stock units and the weighted-average periods over which the compensation cost is expected to be recognized are shown in the following table. December 31, 2019 Unrecognized Compensation Cost (In millions) Weighted Average to be Recognized (In years) Performance units: Total shareholder return $ 8.7 1.67 Earnings per share 0.8 1.00 Total performance units 9.5 Restricted stock units 1.5 1.98 Total unrecognized compensation cost $ 11.0

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Information [Abstract]
Cash Flow, Supplemental Disclosures [Text Block]	Supplemental Cash Flow Information The following table presents information about investing and financing activities that affected recognized assets and liabilities but did not result in cash receipts or payments. Cash paid for interest, net of interest capitalized, and cash paid for income taxes, net of income tax refunds are also presented in the table. Year Ended December 31 (In millions) 2019 2018 2017 NON-CASH INVESTING AND FINANCING ACTIVITIES Power plant long-term service agreement $ 28.9 $ (9.2) $ (2.6) SUPPLEMENTAL CASH FLOW INFORMATION Cash paid during the period for: Interest (net of interest capitalized) (A) $ 152.2 $ 153.8 $ 139.6 Income taxes (net of income tax refunds) $ 5.5 $ 2.8 $ (16.0)

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Taxes [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes Income Tax Expense (Benefit) The items comprising income tax expense (benefit) are as follows: Year Ended December 31 (In millions) 2019 2018 2017 Provision (benefit) for current income taxes: Federal $ (6.4) $ (1.9) $ 4.9 State 5.1 (4.4) (4.2) Total provision (benefit) for current income taxes (1.3) (6.3) 0.7 Provision (benefit) for deferred income taxes, net: Federal 48.5 74.7 (75.9) State (17.4) 3.7 26.0 Total provision (benefit) for deferred income taxes, net 31.1 78.4 (49.9) Deferred federal investment tax credits, net — 0.1 (0.1) Total income tax expense (benefit) $ 29.8 $ 72.2 $ (49.3) The Company files consolidated income tax returns in the U.S. federal jurisdiction and various state jurisdictions. With few exceptions, the Company is no longer subject to U.S. federal tax or state and local examinations by tax authorities for years prior to 2016. Income taxes are generally allocated to each company in the affiliated group based on its stand-alone taxable income or loss. Federal investment tax credits previously claimed on electric utility property have been deferred and will be amortized to income over the life of the related property. Additionally, OG&E earns federal tax credits associated with production from its wind facilities. Oklahoma production and investment state tax credits are also earned on investments in electric and solar generating facilities which further reduce OG&E's effective tax rate. The following schedule reconciles the statutory tax rates to the effective income tax rate: Year Ended December 31 2019 2018 2017 Statutory federal tax rate 21.0 % 21.0 % 35.0 % Executive compensation limitation 0.2 0.2 — Federal renewable energy credit (A) (6.0) (5.1) (4.8) Amortization of net unfunded deferred taxes (4.5) (2.1) 0.7 State income taxes, net of federal income tax benefit (1.2) 0.4 2.0 Stock-based compensation (1.2) — — Remeasurement of state deferred tax liabilities (0.8) (0.4) 0.4 Other (0.7) 0.4 (0.1) 401(k) dividends (0.4) (0.3) (0.5) Federal deferred tax revaluation — 0.4 (41.2) Federal investment tax credits, net — — (0.1) Effective income tax rate 6.4 % 14.5 % (8.6) % (A) Represents credits associated with the production from OG&E's wind farms. The deferred tax provisions are recognized as costs in the ratemaking process by the commissions having jurisdiction over the rates charged by OG&E. The components of Deferred Income Taxes at December 31, 2019 and 2018 were as follows: December 31 (In millions) 2019 2018 Deferred income tax liabilities, net: Accelerated depreciation and other property related differences $ 1,656.8 $ 1,605.3 Investment in Enable 478.2 469.9 Regulatory assets 28.4 17.4 Company Pension Plan 4.1 7.6 Bond redemption-unamortized costs 2.2 2.4 Derivative instruments 1.6 1.7 Other 0.4 1.1 Federal tax credits (238.0) (237.8) Income taxes recoverable from customers, net (229.9) (239.6) State tax credits (185.8) (156.0) Regulatory liabilities (68.1) (78.8) Postretirement medical and life insurance benefits (23.3) (23.6) Asset retirement obligations (19.2) (21.5) Net operating losses (16.6) (20.2) Accrued liabilities (10.7) (12.5) Accrued vacation (2.1) (2.3) Deferred federal investment tax credits (1.8) (1.8) Uncollectible accounts (0.4) (0.4) Total deferred income tax liabilities, net $ 1,375.8 $ 1,310.9 As of December 31, 2019, the Company has classified $16.4 million of unrecognized tax benefits as a reduction of deferred tax assets recorded. Management is currently unaware of any issues under review that could result in significant additional payments, accruals or other material deviation from this amount. Following is a reconciliation of the Company's total gross unrecognized tax benefits as of the years ended December 31, 2019, 2018 and 2017. (In millions) 2019 2018 2017 Balance at January 1 $ 20.7 $ 20.7 $ 20.7 Tax positions related to current year: Additions — — — Balance at December 31 $ 20.7 $ 20.7 $ 20.7 As of each of December 31, 2019, 2018 and 2017, there were $16.4 million of unrecognized tax benefits that, if recognized, would affect the annual effective tax rate. Where applicable, the Company classifies income tax-related interest and penalties as interest expense and other expense, respectively. During the year ended December 31, 2019, there were no income tax-related interest or penalties recorded with regard to uncertain tax positions. The Company sustained federal and state tax operating losses through 2012 caused primarily by bonus depreciation and other book versus tax temporary differences. As a result, the Company had accrued federal and state income tax benefits carrying into 2017, when the remaining federal net operating loss was utilized. State operating losses are being carried forward for utilization in future years. In addition to the tax operating losses, the Company was unable to utilize the various tax credits that were generated during these years. These tax losses and credits are being carried as deferred tax assets and will be utilized in future periods. Under current law, the Company anticipates future taxable income will be sufficient to utilize remaining losses and credits before they begin to expire after 2020. The following table summarizes these carry forwards: (In millions) Carry Forward Amount Deferred Tax Asset Earliest Expiration Date State operating loss $ 371.6 $ 16.6 2030 Federal tax credits $ 238.0 $ 238.0 2032 State tax credits: Oklahoma investment tax credits $ 183.9 $ 145.3 N/A Oklahoma capital investment board credits $ 12.4 $ 12.4 N/A Oklahoma zero emission tax credits $ 34.9 $ 28.0 2020 Louisiana inventory credits $ 0.2 $ 0.1 2020 N/A - not applicable

Common Equity

Common Equity	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Common Equity	Common Equity Automatic Dividend Reinvestment and Stock Purchase Plan The Company issued no shares of common stock under its Automatic Dividend Reinvestment and Stock Purchase Plan in 2019. The Company may, from time to time, issue shares under its Automatic Dividend Reinvestment and Stock Purchase Plan or purchase shares traded on the open market. At December 31, 2019, there were 4,774,442 shares of unissued common stock reserved for issuance under the Company's Automatic Dividend Reinvestment and Stock Purchase Plan. Earnings Per Share Basic earnings per share is calculated by dividing net income attributable to the Company by the weighted average number of the Company's common shares outstanding during the period. In the calculation of diluted earnings per share, weighted average shares outstanding are increased for additional shares that would be outstanding if potentially dilutive securities were converted to common stock. Potentially dilutive securities for the Company consist of performance units and restricted stock units. The following table calculates basic and diluted earnings per share for the Company. (In millions except per share data) 2019 2018 2017 Net income $ 433.6 $ 425.5 $ 619.0 Average common shares outstanding: Basic average common shares outstanding 200.1 199.7 199.7 Effect of dilutive securities: Contingently issuable shares (performance and restricted stock units) 0.6 0.8 0.3 Diluted average common shares outstanding 200.7 200.5 200.0 Basic earnings per average common share $ 2.17 $ 2.13 $ 3.10 Diluted earnings per average common share $ 2.16 $ 2.12 $ 3.10 Anti-dilutive shares excluded from earnings per share calculation — — — Dividend Restrictions The Company's Certificate of Incorporation places restrictions on the amount of common stock dividends it can pay when preferred stock is outstanding. Before the Company can pay any dividends on its common stock, the holders of any of its preferred stock that may be outstanding are entitled to receive their dividends at the respective rates as may be provided for the shares of their series. As there is no preferred stock outstanding, that restriction did not place any effective limit on the Company's ability to pay dividends to its shareholders. The Company utilizes receipts from its equity investment in Enable and dividends from OG&E to pay dividends to its shareholders. Enable's partnership agreement requires that it distribute all "available cash," as defined as cash on hand at the end of a quarter after the payment of expenses and the establishment of cash reserves and cash on hand resulting from working capital borrowings made after the end of the quarter. Pursuant to the leverage restriction in the Company's revolving credit agreement, the Company must maintain a percentage of debt to total capitalization at a level that does not exceed 65 percent. The payment of cash dividends indirectly results in an increase in the percentage of debt to total capitalization, which results in the restriction of approximately $661.4 million of the Company's retained earnings from being paid out in dividends. Accordingly, approximately $2.4 billion of the Company's retained earnings as of December 31, 2019 are unrestricted for the payment of dividends.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2019
Long-term Debt, Unclassified [Abstract]
Long-Term Debt	Long-Term Debt A summary of the Company's long-term debt is included in the Consolidated Statements of Capitalization. The Company has no long-term debt maturing in the next five years. At December 31, 2019, the Company was in compliance with all of its debt agreements. The Company has previously incurred costs related to debt refinancing. Unamortized loss on reacquired debt is classified as a Non-Current Regulatory Asset. Unamortized debt expense and unamortized premium and discount on long-term debt are classified as Long-Term Debt in the Consolidated Balance Sheets and are being amortized over the life of the respective debt. OG&E Industrial Authority Bonds OG&E has tax-exempt pollution control bonds with optional redemption provisions that allow the holders to request repayment of the bonds on any business day. The bonds, which can be tendered at the option of the holder during the next 12 months, are as follows: Series Date Due Amount (In millions) 1.20% - 2.50% Garfield Industrial Authority, January 1, 2025 $ 47.0 1.19% - 2.35% Muskogee Industrial Authority, January 1, 2025 32.4 1.20% - 2.48% Muskogee Industrial Authority, June 1, 2027 56.0 Total (redeemable during next 12 months) $ 135.4 All of these bonds are subject to an optional tender at the request of the holders, at 100 percent of the principal amount, together with accrued and unpaid interest to the date of purchase. The bond holders, on any business day, can request repayment of the bond by delivering an irrevocable notice to the tender agent stating the principal amount of the bond, payment instructions for the purchase price and the business day the bond is to be purchased. The repayment option may only be exercised by the holder of a bond for the principal amount. When a tender notice has been received by the trustee, a third-party remarketing agent for the bonds will attempt to remarket any bonds tendered for purchase. This process occurs once per week. Since the original issuance of these series of bonds in 1995 and 1997, the remarketing agent has successfully remarketed all tendered bonds. If the remarketing agent is unable to remarket any such bonds, OG&E is obligated to repurchase such unremarketed bonds. As OG&E has both the intent and ability to refinance the bonds on a long-term basis and such ability is supported by an ability to consummate the refinancing, the bonds are classified as Long-Term Debt in the Company's Consolidated Financial Statements. OG&E believes that it has sufficient liquidity to meet these obligations. Issuance of Long-Term Debt In June 2019, OG&E issued $300.0 million of 3.30 percent senior notes due March 15, 2030. The proceeds from the issuance were added to OG&E's general funds to be used for general corporate purposes, including to repay short-term debt (including debt pertaining to the acquisition of the River Valley plant) and to fund ongoing capital expenditures and working capital.

Short-Term Debt and Credit Faci

Short-Term Debt and Credit Facilities	12 Months Ended
	Dec. 31, 2019
Short-term Debt [Abstract]
Short-Term Debt and Credit Facilities	Short-Term Debt and Credit Facilities The Company borrows on a short-term basis, as necessary, by the issuance of commercial paper and by borrowings under its revolving credit agreement. As of December 31, 2019, the Company had $112.0 million short-term debt as compared to no short-term debt at December 31, 2018. The following table provides information regarding the Company's revolving credit agreements at December 31, 2019. Aggregate Amount Weighted-Average Entity Commitment Outstanding (A) Interest Rate Expiration (In millions) OGE Energy (B) $ 450.0 $ 112.0 2.06 % (D) March 8, 2023 OG&E (C) 450.0 0.3 1.00 % (D) March 8, 2023 Total $ 900.0 $ 112.3 2.06 % (A) Includes direct borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit at December 31, 2019. (B) This bank facility is available to back up the Company's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility. (C) This bank facility is available to back up OG&E's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility. (D) Represents the weighted-average interest rate for the outstanding borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit. The Company and OG&E's credit facilities each have a financial covenant requiring that the respective borrower maintain a maximum debt to capitalization ratio of 65 percent, as defined in each such facility. The Company and OG&E's facilities each also contain covenants which restrict the respective borrower and certain of its subsidiaries in respect of, among other things, mergers and consolidations, sales of all or substantially all assets, incurrence of liens and transactions with affiliates. The Company and OG&E's facilities are each subject to acceleration upon the occurrence of any default, including, among others, payment defaults on such facilities, breach of representations, warranties and covenants, acceleration of indebtedness (other than intercompany and non-recourse indebtedness) of $100.0 million or more in the aggregate, change of control (as defined in each such facility), nonpayment of uninsured judgments in excess of $100.0 million and the occurrence of certain Employee Retirement Income Security Act and bankruptcy events, subject where applicable to specified cure periods. The Company's ability to access the commercial paper market could be adversely impacted by a credit ratings downgrade or major market disruptions. Pricing grids associated with the Company's credit facilities could cause annual fees and borrowing rates to increase if an adverse rating impact occurs. The impact of any future downgrade could include an increase in the costs of the Company's short-term borrowings, but a reduction in the Company's credit ratings would not result in any defaults or accelerations. Any future downgrade could also lead to higher long-term borrowing costs and, if below investment grade, would require the Company to post collateral or letters of credit.

Retirement Plans and Postretire

Retirement Plans and Postretirement Benefit Plans	12 Months Ended
	Dec. 31, 2019
Retirement Plans and Postretirement Benefit Plans [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	Retirement Plans and Postretirement Benefit Plans Pension Plan and Restoration of Retirement Income Plan It is the Company's policy to fund the Pension Plan on a current basis based on the net periodic pension expense as determined by the Company's actuarial consultants. Such contributions are intended to provide not only for benefits attributed to service to date but also for those expected to be earned in the future. The Company made a $20.0 million and $15.0 million contribution to its Pension Plan in 2019 and 2018, respectively. The Company has not determined whether it will need to make any contributions to the Pension Plan in 2020. Any contribution to the Pension Plan during 2020 would be a discretionary contribution, anticipated to be in the form of cash, and is not required to satisfy the minimum regulatory funding requirement specified by the Employee Retirement Income Security Act of 1974, as amended. The Company could be required to make additional contributions if the value of its pension trust and postretirement benefit plan trust assets are adversely impacted by a major market disruption in the future. In accordance with ASC Topic 715, "Compensation - Retirement Benefits," a one-time settlement charge is required to be recorded by an organization when lump sum payments or other settlements that relieve the organization from the responsibility for the pension benefit obligation during the plan year exceed the service cost and interest cost components of the organization's net periodic pension cost. During 2019, 2018 and 2017, the Company experienced an increase in both the number of employees electing to retire and the amount of lump sum payments paid to such employees upon retirement, which resulted in the Company recording pension plan settlement charges as presented in the net periodic benefit cost table below. The pension settlement charges did not require a cash outlay by the Company and did not increase the Company's total pension expense over time, as the charges were an acceleration of costs that otherwise would be recognized as pension expense in future periods. The Company provides a Restoration of Retirement Income Plan to those participants in the Company's Pension Plan whose benefits are subject to certain limitations of the Code. Participants in the Restoration of Retirement Income Plan receive the same benefits that they would have received under the Company's Pension Plan in the absence of limitations imposed by the federal tax laws. The Restoration of Retirement Income Plan is intended to be an unfunded plan. Obligations and Funded Status The following table presents the status of the Company's Pension Plan, the Restoration of Retirement Income Plan and the postretirement benefit plans for 2019 and 2018. These amounts have been recorded in Accrued Benefit Obligations with the offset in Accumulated Other Comprehensive Loss (except OG&E's portion, which is recorded as a regulatory asset as discussed in Note 1) in the Company's Consolidated Balance Sheets. The amounts in Accumulated Other Comprehensive Loss and those recorded as a regulatory asset represent a net periodic benefit cost to be recognized in the Consolidated Statements of Income in future periods. The benefit obligation for the Company's Pension Plan and the Restoration of Retirement Income Plan represents the projected benefit obligation, while the benefit obligation for the postretirement benefit plans represents the accumulated postretirement benefit obligation. The accumulated postretirement benefit obligation for the Company's Pension Plan and Restoration of Retirement Income Plan differs from the projected benefit obligation in that the former includes no assumption about future compensation levels. The accumulated postretirement benefit obligation for the Pension Plan and the Restoration of Retirement Income Plan at December 31, 2019 was $563.3 million and $8.1 million, respectively. The accumulated postretirement benefit obligation for the Pension Plan and the Restoration of Retirement Income Plan at December 31, 2018 was $561.9 million and $7.8 million, respectively. The details of the funded status of the Pension Plan, the Restoration of Retirement Income Plan and the postretirement benefit plans and the amounts included in the Consolidated Balance Sheets are included in the following table. Pension Plan Restoration of Retirement Postretirement December 31 (In millions) 2019 2018 2019 2018 2019 2018 Change in benefit obligation Beginning obligations $ 615.9 $ 687.5 $ 9.6 $ 8.1 $ 135.8 $ 149.4 Service cost 12.9 14.9 0.5 0.4 0.2 0.3 Interest cost 20.7 23.8 0.4 0.3 5.6 5.4 Plan settlements (83.1) (73.7) (1.2) (2.0) — — Plan amendments — — 0.3 — — — Participants' contributions — — — — 4.1 3.8 Actuarial losses (gains) 64.3 (22.0) 0.7 2.8 2.9 (9.6) Benefits paid (14.6) (14.6) — — (12.1) (13.5) Ending obligations $ 616.1 $ 615.9 $ 10.3 $ 9.6 $ 136.5 $ 135.8 Change in plans' assets Beginning fair value $ 522.8 $ 635.3 $ — $ — $ 45.3 $ 50.2 Actual return on plans' assets 85.2 (39.2) — — 4.6 (0.6) Employer contributions 20.0 15.0 1.2 2.0 5.1 5.4 Plan settlements (83.1) (73.7) (1.2) (2.0) — — Participants' contributions — — — — 4.1 3.8 Benefits paid (14.6) (14.6) — — (12.1) (13.5) Ending fair value $ 530.3 $ 522.8 $ — $ — $ 47.0 $ 45.3 Funded status at end of year $ (85.8) $ (93.1) $ (10.3) $ (9.6) $ (89.5) $ (90.5) Net Periodic Benefit Cost The following table presents the net periodic benefit cost components, before consideration of capitalized amounts, of the Company's Pension Plan, Restoration of Retirement Income Plan and postretirement benefit plans that are included in the Consolidated Financial Statements. Service cost is presented within Other Operation and Maintenance, and interest cost, expected return on plan assets, amortization of net loss, amortization of unrecognized prior service cost and settlement cost are presented within Other Net Periodic Benefit Expense in the Company's Consolidated Statements of Income. OG&E recovers specific amounts of pension and postretirement medical costs in rates approved in its Oklahoma rate reviews. In accordance with approved orders, OG&E defers the difference between actual pension and postretirement medical expenses and the amount approved in its last Oklahoma rate review as a regulatory asset or regulatory liability. These amounts have been recorded in the Pension tracker in the regulatory assets and liabilities table in Note 1 and within Other Net Periodic Benefit Expense in the Company's Consolidated Statements of Income. Pension Plan Restoration of Retirement Postretirement Benefit Plans Year Ended December 31 (In millions) 2019 2018 2017 2019 2018 2017 2019 2018 2017 Service cost $ 12.9 $ 14.9 $ 15.5 $ 0.5 $ 0.4 $ 0.3 $ 0.2 $ 0.3 $ 0.6 Interest cost 20.7 23.8 26.2 0.4 0.3 0.3 5.6 5.4 7.2 Expected return on plan assets (36.1) (44.1) (42.6) — — — (1.9) (2.0) (2.2) Amortization of net loss 17.3 16.2 17.4 0.5 0.7 0.4 2.0 3.8 2.0 Amortization of unrecognized prior service cost (A) — — (0.1) — 0.1 0.1 (8.4) (8.4) (3.5) Settlement cost 27.6 25.1 15.3 0.5 1.0 — — — 0.6 Total net periodic benefit cost 42.4 35.9 31.7 1.9 2.5 1.1 (2.5) (0.9) 4.7 Less: Amount paid by unconsolidated affiliates 2.9 2.5 4.3 0.1 0.1 — (0.6) (0.5) 0.3 Net periodic benefit cost $ 39.5 $ 33.4 $ 27.4 $ 1.8 $ 2.4 $ 1.1 $ (1.9) $ (0.4) $ 4.4 (A) Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment. In addition to the net periodic benefit cost amounts recognized, as presented in the table above, for the Pension and Restoration of Retirement Income Plans in 2019, 2018 and 2017, the Company recognized the following: Year Ended December 31 (In millions) 2019 2018 2017 Decrease of pension expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) $ (16.1) $ (14.1) $ (2.3) Deferral of pension expense related to pension settlement charges: Oklahoma jurisdiction (A) $ 17.9 $ 22.1 $ 13.2 Arkansas jurisdiction (A) $ 1.7 $ 2.1 $ 1.1 (A) Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1. In addition to the net periodic benefit income and cost amounts recognized, as presented in the table above, for the postretirement benefit plans in 2019, 2018 and 2017, the Company recognized the following: Year Ended December 31 (In millions) 2019 2018 2017 Increase of postretirement expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) $ 1.0 $ 4.4 $ 6.2 (A) Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1. (In millions) 2019 2018 2017 Capitalized portion of net periodic pension benefit cost $ 3.6 $ 3.8 $ 4.4 Capitalized portion of net periodic postretirement benefit cost $ 0.2 $ 0.2 $ 1.2 Rate Assumptions Pension Plan and Postretirement Year Ended December 31 2019 2018 2017 2019 2018 2017 Assumptions to determine benefit obligations: Discount rate 3.15 % 4.20 % 3.60 % 3.25 % 4.30 % 3.70 % Rate of compensation increase 4.20 % 4.20 % 4.20 % N/A N/A N/A Assumptions to determine net periodic benefit cost: Discount rate 3.63 % 3.73 % 4.00 % 4.30 % 3.70 % 4.20 % Expected return on plan assets 7.50 % 7.50 % 7.50 % 4.00 % 4.00 % 4.00 % Rate of compensation increase 4.20 % 4.20 % 4.20 % N/A N/A 4.20 % N/A - not applicable The discount rate used to compute the present value of plan liabilities is based generally on rates of high-grade corporate bonds with maturities similar to the average period over which benefits will be paid. The discount rate used to determine net benefit cost for the current year is the same discount rate used to determine the benefit obligation as of the previous year's balance sheet date, unless a plan settlement occurs during the current year that requires an updated discount rate for net periodic cost measurement. For 2019 and 2018, the Pension Plan discount rates used to determine net periodic benefit cost are disclosed on a weighted-average basis. The overall expected rate of return on plan assets assumption was 7.50 percent in both 2019 and 2018, which was used in determining net periodic benefit cost due to recent returns on the Company's long-term investment portfolio. The rate of return on plan assets assumption is the average long-term rate of earnings expected on the funds currently invested and to be invested for the purpose of providing benefits specified by the Pension Plan or postretirement benefit plans. This assumption is reexamined at least annually and updated as necessary. The rate of return on plan assets assumption reflects a combination of historical return analysis, forward-looking return expectations and the plans' current and expected asset allocation. The assumed health care cost trend rates have a significant effect on the amounts reported for postretirement medical benefit plans. Future health care cost trend rates are assumed to be 7.00 percent in 2020 with the rates trending downward to 4.50 percent by 2030. The effects of a one-percentage point change in the assumed health care cost trend rate are presented in the following tables. ONE-PERCENTAGE POINT INCREASE Year Ended December 31 (In millions) 2019 2018 2017 Effect on aggregate of the service and interest cost components $ — $ — $ — Effect on accumulated postretirement benefit obligations $ 0.1 $ 0.1 $ 0.1 ONE-PERCENTAGE POINT DECREASE Year Ended December 31 (In millions) 2019 2018 2017 Effect on aggregate of the service and interest cost components $ — $ — $ — Effect on accumulated postretirement benefit obligations $ 0.3 $ 0.3 $ 0.3 Pension Plan Pension Plan Investments, Policies and Strategies The Pension Plan assets are held in a trust which follows an investment policy and strategy designed to reduce the funded status volatility of the Plan by utilizing liability driven investing. The purpose of liability-driven investing is to structure the asset portfolio to more closely resemble the pension liability and thereby more effectively hedge against changes in the liability. The investment policy follows a glide path approach that shifts a higher portfolio weighting to fixed income as the Plan's funded status increases. The table below sets forth the targeted fixed income and equity allocations at different funded status levels. Projected Benefit Obligation Funded Status Thresholds <90% 95% 100% 105% 110% 115% 120% Fixed income 50% 58% 65% 73% 80% 85% 90% Equity 50% 42% 35% 27% 20% 15% 10% Total 100% 100% 100% 100% 100% 100% 100% Within the portfolio's overall allocation to equities, the funds are allocated according to the guidelines in the table below. Asset Class Target Allocation Minimum Maximum Domestic Large Cap Equity 40% 35% 60% Domestic Mid-Cap Equity 15% 5% 25% Domestic Small-Cap Equity 25% 5% 30% International Equity 20% 10% 30% The Company has retained an investment consultant responsible for the general investment oversight, analysis, monitoring investment guideline compliance and providing quarterly reports to certain of the Company's members and the Company's Investment Committee. The various investment managers used by the trust operate within the general operating objectives as established in the investment policy and within the specific guidelines established for each investment manager's respective portfolio. The portfolio is rebalanced at least on an annual basis to bring the asset allocations of various managers in line with the target asset allocation listed above. More frequent rebalancing may occur if there are dramatic price movements in the financial markets which may cause the trust's exposure to any asset class to exceed or fall below the established allowable guidelines. To evaluate the progress of the portfolio, investment performance is reviewed quarterly. It is, however, expected that performance goals will be met over a full market cycle, normally defined as a three to five year period. Analysis of performance is within the context of the prevailing investment environment and the advisors' investment style. The goal of the trust is to provide a rate of return consistently from three percent to five percent over the rate of inflation (as measured by the national Consumer Price Index) on a fee adjusted basis over a typical market cycle of no less than three years and no more than five years. Each investment manager is expected to outperform its respective benchmark. Below is a list of each asset class utilized with appropriate comparative benchmark(s) each manager is evaluated against: Asset Class Comparative Benchmark(s) Active Duration Fixed Income Bloomberg Barclays Aggregate Long Duration Fixed Income Duration blended Barclays Long Government/Credit & Barclays Universal Equity Index Standard & Poor's 500 Index Mid-Cap Equity Russell Midcap Index Russell Midcap Value Index Small-Cap Equity Russell 2000 Index Russell 2000 Value Index International Equity Morgan Stanley Capital International ACWI ex-U.S. The fixed income managers are expected to use discretion over the asset mix of the trust assets in their efforts to maximize risk-adjusted performance. Exposure to any single issuer, other than the U.S. government, its agencies or its instrumentalities (which have no limits), is limited to five percent of the fixed income portfolio as measured by market value. At least 75 percent of the invested assets must possess an investment-grade rating at or above Baa3 or BBB- by Moody's Investors Service, S&P's Global Ratings or Fitch Ratings. The portfolio may invest up to 10 percent of the portfolio's market value in convertible bonds as long as the securities purchased meet the quality guidelines. A portfolio may invest up to 15 percent of the portfolio's market value in private placement, including 144A securities with or without registration rights and allow for futures to be traded in the portfolio. The purchase of any of the Company's equity, debt or other securities is prohibited. The domestic value equity managers focus on stocks that the manager believes are undervalued in price and earn an average or less than average return on assets and often pays out higher than average dividend payments. The domestic growth equity manager will invest primarily in growth companies which consistently experience above average growth in earnings and sales, earn a high return on assets and reinvest cash flow into existing business. The domestic mid-cap equity portfolio manager focuses on companies with market capitalizations lower than the average company traded on the public exchanges with the following characteristics: price/earnings ratio at or near the Russell Midcap Index, small dividend yield, return on equity at or near the Russell Midcap Index and an earnings per share growth rate at or near the Russell Midcap Index. The domestic small-cap equity manager will purchase shares of companies with market capitalizations lower than the average company traded on the public exchanges with the following characteristics: price/earnings ratio at or near the Russell 2000, small dividend yield, return on equity at or near the Russell 2000 and an earnings per share growth rate at or near the Russell 2000. The international global equity manager invests primarily in non-dollar denominated equity securities. Investing internationally diversifies the overall trust across the global equity markets. The manager is required to operate under certain restrictions including regional constraints, diversification requirements and percentage of U.S. securities. The Morgan Stanley Capital International All Country World ex-U.S. Index is the benchmark for comparative performance purposes. The Morgan Stanley Capital International All Country World ex-U.S. Index is a market value weighted index designed to measure the combined equity market performance of developed and emerging markets countries, excluding the U.S. All of the equities which are purchased for the international portfolio are thoroughly researched. All securities are freely traded on a recognized stock exchange, and there are no over-the-counter derivatives. The following investment categories are excluded: options (other than traded currency options), commodities, futures (other than currency futures or currency hedging), short sales/margin purchases, private placements, unlisted securities and real estate (but not real estate shares). For all domestic equity investment managers, no more than five percent can be invested in any one stock at the time of purchase and no more than 10 percent after accounting for price appreciation. Options or financial futures may not be purchased unless prior approval of the Company's Investment Committee is received. The purchase of securities on margin is prohibited as is securities lending. Private placement or venture capital may not be purchased. All interest and dividend payments must be swept on a daily basis into a short-term money market fund for re-deployment. The purchase of any of the Company's equity, debt or other securities is prohibited. The purchase of equity or debt issues of the portfolio manager's organization is also prohibited. The aggregate positions in any company may not exceed one percent of the fair market value of its outstanding stock. Pension Plan Investments The following tables summarize the Pension Plan's investments that are measured at fair value on a recurring basis at December 31, 2019 and 2018. There were no Level 3 investments held by the Pension Plan at December 31, 2019 and 2018. (In millions) December 31, 2019 Level 1 Level 2 Net Asset Value (A) Common stocks $ 202.0 $ 202.0 $ — $ — U.S. Treasury notes and bonds (B) 134.8 134.8 — — Mortgage- and asset-backed securities 45.8 — 45.8 — Corporate fixed income and other securities 130.5 — 130.5 — Commingled fund (C) 23.9 — — 23.9 Foreign government bonds 3.0 — 3.0 — U.S. municipal bonds 1.1 — 1.1 — Money market fund 7.5 — — 7.5 Mutual fund 2.4 2.4 — — Preferred stocks 0.7 0.7 — — Futures: U.S. Treasury futures (receivable) 22.9 — 22.9 — U.S. Treasury futures (payable) (10.9) — (10.9) — Cash collateral 0.6 0.6 — — Forward contracts: Receivable (foreign currency) 0.1 — 0.1 — Total Pension Plan investments 564.4 $ 340.5 $ 192.5 $ 31.4 Interest and dividends receivable 2.4 Payable to broker for securities purchased (36.5) Total Pension Plan assets $ 530.3 (A) GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy. (B) This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher. (C) This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets. (In millions) December 31, 2018 Level 1 Level 2 Net Asset Value (A) Common stocks $ 169.3 $ 169.3 $ — $ — U.S. Treasury notes and bonds (B) 137.9 137.9 — — Mortgage- and asset-backed securities 65.9 — 65.9 — Corporate fixed income and other securities 143.2 — 143.2 — Commingled fund (C) 19.7 — — 19.7 Foreign government bonds 4.4 — 4.4 — U.S. municipal bonds 0.6 — 0.6 — Money market fund 0.3 — — 0.3 Mutual fund 8.0 8.0 — — Futures: U.S. Treasury futures (receivable) 27.0 — 27.0 — U.S. Treasury futures (payable) (20.4) — (20.4) — Cash collateral 0.7 0.7 — — Forward contracts: Receivable (foreign currency) 0.1 — 0.1 — Total Pension Plan investments 556.7 $ 315.9 $ 220.8 $ 20.0 Interest and dividends receivable 3.0 Payable to broker for securities purchased (36.9) Total Pension Plan assets $ 522.8 (A) GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy. (B) This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher. (C) This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets. As defined in the fair value hierarchy, Level 1 inputs are quoted prices in active markets for identical unrestricted assets or liabilities that are accessible by the Pension Plan at the measurement date. Level 2 inputs are inputs other than quoted prices in active markets included within Level 1 that are either directly or indirectly observable at the reporting date for the asset or liability for substantially the full term of the asset or liability. Level 2 inputs include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. Level 3 inputs are prices or valuation techniques for the asset or liability that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). Unobservable inputs reflect the Plan's own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk). Expected Benefit Payments The following table summarizes the benefit payments the Company expects to pay related to OGE Energy's Pension Plan and Restoration of Retirement Income Plan. These expected benefits are based on the same assumptions used to measure the Company's benefit obligation at the end of the year and include benefits attributable to estimated future employee service. (In millions) Projected Benefit Payments 2020 $ 58.4 2021 $ 56.8 2022 $ 56.2 2023 $ 55.7 2024 $ 56.6 After 2024 $ 249.4 Postretirement Benefit Plans In addition to providing pension benefits, the Company provides certain medical and life insurance benefits for eligible retired members. Regular, full-time, active employees hired prior to February 1, 2000 whose age and years of credited service total or exceed 80 or have attained at least age 55 with 10 or more years of service at the time of retirement are entitled to postretirement medical benefits, while employees hired on or after February 1, 2000 are not entitled to postretirement medical benefits. Eligible retirees must contribute such amount as the Company specifies from time to time toward the cost of coverage for postretirement benefits. The benefits are subject to deductibles, co-payment provisions and other limitations. OG&E charges postretirement benefit costs to expense and includes an annual amount as a component of the cost-of-service in future ratemaking proceedings. The Company's contribution to the medical costs for pre-65 aged eligible retirees are fixed at the 2011 level, and the Company covers future annual medical inflationary cost increases up to five percent. Increases in excess of five percent annually are covered by the pre-65 aged retiree in the form of premium increases. The Company provides Medicare-eligible retirees and their Medicare-eligible spouses an annual fixed contribution to a Company-sponsored health reimbursement arrangement. Medicare-eligible retirees are able to purchase individual insurance policies supplemental to Medicare through a third-party administrator and use their health reimbursement arrangement funds for reimbursement of medical premiums and other eligible medical expenses. Postretirement Plans Investments The following tables summarize the postretirement benefit plans' investments that are measured at fair value on a recurring basis at December 31, 2019 and 2018. There were no Level 2 investments held by the postretirement benefit plans at December 31, 2019 and 2018. (In millions) December 31, 2019 Level 1 Level 3 Group retiree medical insurance contract $ 34.8 $ — $ 34.8 Mutual funds 10.9 10.9 — Money market fund 1.2 1.2 — Total plan investments $ 46.9 $ 12.1 $ 34.8 (In millions) December 31, 2018 Level 1 Level 3 Group retiree medical insurance contract $ 36.0 $ — $ 36.0 Mutual funds 8.9 8.9 — Cash 0.9 0.9 — Total plan investments $ 45.8 $ 9.8 $ 36.0 The group retiree medical insurance contract invests in a pool of common stocks, bonds and money market accounts, of which a significant portion is comprised of mortgage-backed securities. The unobservable input included in the valuation of the contract includes the approach for determining the allocation of the postretirement benefit plans' pro-rata share of the total assets in the contract. The following table summarizes the postretirement benefit plans' investments that are measured at fair value on a recurring basis using significant unobservable inputs (Level 3). Year Ended December 31 (In millions) 2019 Group retiree medical insurance contract: Beginning balance $ 36.0 Claims paid (3.8) Investment fees (0.1) Net unrealized gains related to instruments held at the reporting date 1.4 Interest income 0.8 Dividend income 0.5 Ending balance $ 34.8 Medicare Prescription Drug, Improvement and Modernization Act of 2003 The Medicare Prescription Drug, Improvement and Modernization Act of 2003 expanded coverage for prescription drugs. The following table summarizes the gross benefit payments the Company expects to pay related to its postretirement benefit plans, including prescription drug benefits. (In millions) Gross Projected 2020 $ 11.2 2021 $ 11.2 2022 $ 11.1 2023 $ 9.5 2024 $ 9.4 After 2024 $ 42.3 Post-Employment Benefit Plan Disabled employees receiving benefits from the Company's Group Long-Term Disability Plan are entitled to continue participating in the Company's Medical Plan along with their dependents. The post-employment benefit obligation represents the actuarial present value of estimated future medical benefits that are attributed to employee service rendered prior to the date as of which such information is presented. The obligation also includes future medical benefits expected to be paid to current employees participating in the Company's Group Long-Term Disability Plan and their dependents, as defined in the Company's Medical Plan. The post-employment benefit obligation is determined by an actuary on a basis similar to the accumulated postretirement benefit obligation. The estimated future medical benefits are projected to grow with expected future medical cost trend rates and are discounted for interest at the discount rate and for the probability that the participant will discontinue receiving benefits from the Company's Group Long-Term Disability Plan due to death, recovery from disability or eligibility for retiree medical benefits. The Company's post-employment benefit obligation was $2.1 million and $1.9 million at December 31, 2019 and 2018, respectively. 401(k) Plan The Company provides a 401(k) Plan, and each regular full-time employee of the Company or a participating affiliate is eligible to participate in the 401(k) Plan immediately. All other employees of the Company or a participating affiliate are eligible to become participants in the 401(k) Plan after completing one year of service as defined in the 401(k) Plan. Participants may contribute each pay period any whole percentage between two percent and 19 percent of their compensation, as defined in the 401(k) Plan, for that pay period. Participants who have reached age 50 before the close of a year are allowed to make additional contributions referred to as "Catch-Up Contributions," subject to certain limitations of the Code. Participants may designate, at their discretion, all or any portion of their contributions as: (i) a before-tax contribution under Section 401(k) of the Code subject to the limitations thereof, (ii) a contribution made on a non-Roth after-tax basis or (iii) a Roth contribution. The 401(k) Plan also includes an eligible automatic contribution arrangement and provides for a qualified default investment alternative consistent with the U.S. Department of Labor regulations. Participants may elect, in accordance with the 401(k) Plan procedures, to have their future salary deferral rate to be automatically increased annually on a date and in an amount as specified by the participant in such election. For employees hired or rehired on or after December 1, 2009, the Company contributes to the 401(k) Plan, on behalf of each participant, 200 percent of the participant's contributions up to five percent of compensation. No Company contributions are made with respect to a participant's Catch-Up Contributions, rollover contributions or with respect to a participant's contributions based on overtime payments, pay-in-lieu of overtime for exempt personnel, special lump-sum recognition awards and lump-sum merit awards included in compensation for determining the amount of participant contributions. Once made, the Company's contribution may be directed to any available investment option in the 401(k) Plan. The Company match contributions vest over a three-year period. After two years of service, participants become 20 percent vested in their Company contribution account and become fully vested on completing three years of service. In addition, participants fully vest when they are eligible for normal or early retirement under the Pension Plan requirements, in the event of their termination due to death or permanent disability or upon attainment of age 65 while employed by the Company or its affiliates. The Company contributed $14.4 million, $13.2 million and $13.2 million in 2019, 2018 and 2017, respectively, to the 401(k) Plan. Deferred Compensation Plan The Company provides a nonqualified deferred compensation plan which is intended to be an unfunded plan. The plan's primary purpose is to provide a tax-deferred capital accumulation vehicle for a select group of management, highly compensated employees and non-employee members of the Board of Directors of the Company and to supplement such employees' 401(k) Plan contributions as well as offering this plan to be competitive in the marketplace. Eligible employees who enroll in the plan have the following deferral options: (i) eligible employees may elect to defer up to a maximum of 70 percent of base salary and 100 percent of annual bonus awards or (ii) eligible employees may elect a deferral percentage of base salary and bonus awards based on the de

Report of Business Segments

Report of Business Segments	12 Months Ended
	Dec. 31, 2019
Segment Reporting Information [Line Items]
Report of Business Segments	Report of Business Segments The Company reports its operations in two business segments: (i) the electric utility segment, which is engaged in the generation, transmission, distribution and sale of electric energy and (ii) natural gas midstream operations segment. Other operations primarily includes the operations of the holding company. Intersegment revenues are recorded at prices comparable to those of unaffiliated customers and are affected by regulatory considerations. The following tables summarize the results of the Company's business segments for the years ended December 31, 2019, 2018 and 2017. 2019 Electric Utility Natural Gas Midstream Operations Other Eliminations Total (In millions) Operating revenues $ 2,231.6 $ — $ — $ — $ 2,231.6 Cost of sales 786.9 — — — 786.9 Other operation and maintenance 492.5 2.8 (3.5) — 491.8 Depreciation and amortization 355.0 — — — 355.0 Taxes other than income 89.5 0.4 3.7 — 93.6 Operating income (loss) 507.7 (3.2) (0.2) — 504.3 Equity in earnings of unconsolidated affiliates — 113.9 — — 113.9 Other income (expense) 3.1 (8.6) 2.2 (3.6) (6.9) Interest expense 140.5 — 11.0 (3.6) 147.9 Income tax expense (benefit) 20.1 20.7 (11.0) — 29.8 Net income $ 350.2 $ 81.4 $ 2.0 $ — $ 433.6 Investment in unconsolidated affiliates $ — $ 1,132.9 $ 18.6 $ — $ 1,151.5 Total assets $ 10,076.6 $ 1,135.4 $ 107.0 $ (294.7) $ 11,024.3 Capital expenditures $ 635.5 $ — $ — $ — $ 635.5 2018 Electric Utility Natural Gas Midstream Operations Other Eliminations Total (In millions) Operating revenues $ 2,270.3 $ — $ — $ — $ 2,270.3 Cost of sales 892.5 — — — 892.5 Other operation and maintenance 473.8 1.4 (0.6) — 474.6 Depreciation and amortization 321.6 — — — 321.6 Taxes other than income 88.2 0.6 3.2 — 92.0 Operating income (loss) 494.2 (2.0) (2.6) — 489.6 Equity in earnings of unconsolidated affiliates — 152.8 — — 152.8 Other income (expense) 25.6 (4.9) (3.4) (6.0) 11.3 Interest expense 151.8 — 10.2 (6.0) 156.0 Income tax expense (benefit) 40.0 37.1 (4.9) — 72.2 Net income (loss) $ 328.0 $ 108.8 $ (11.3) $ — $ 425.5 Investment in unconsolidated affiliates $ — $ 1,166.6 $ 10.9 $ — $ 1,177.5 Total assets $ 9,704.5 $ 1,169.8 $ 184.8 $ (310.5) $ 10,748.6 Capital expenditures $ 573.6 $ — $ — $ — $ 573.6 2017 Electric Utility Natural Gas Midstream Operations Other Eliminations Total (In millions) Operating revenues $ 2,261.1 $ — $ — $ — $ 2,261.1 Cost of sales 897.6 — — — 897.6 Other operation and maintenance 469.8 (0.8) (10.3) — 458.7 Depreciation and amortization 280.9 — 2.6 — 283.5 Taxes other than income 84.8 1.0 3.6 — 89.4 Operating income (loss) 528.0 (0.2) 4.1 — 531.9 Equity in earnings of unconsolidated affiliates — 131.2 — — 131.2 Other income (expense) 57.7 (1.0) (5.4) (0.9) 50.4 Interest expense 138.4 — 6.3 (0.9) 143.8 Income tax expense (benefit) (A) 141.8 (195.2) 4.1 — (49.3) Net income (loss) $ 305.5 $ 325.2 $ (11.7) $ — $ 619.0 Investment in unconsolidated affiliates $ — $ 1,151.9 $ 8.5 $ — $ 1,160.4 Total assets $ 9,255.6 $ 1,155.3 $ 109.1 $ (107.3) $ 10,412.7 Capital expenditures $ 824.1 $ — $ — $ — $ 824.1

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Public Utility Regulatory Policy Act of 1978 OG&E had a QF contract with AES which expired on January 15, 2019 and a QF contract with Oklahoma Cogeneration LLC which expired on August 31, 2019. For the 320 MW AES QF contract and the 120 MW Oklahoma Cogeneration LLC QF contract, OG&E purchased 100 percent of the electricity generated by the QFs. In December 2018, OG&E announced its plan to acquire power plants from AES and Oklahoma Cogeneration LLC, pending regulatory approval, to meet customers' energy needs. In May 2019, OG&E received the necessary approval from the OCC and the FERC and conditional approval from the APSC to acquire both plants. In May 2019, OG&E acquired the power plant from AES, and in August 2019, OG&E acquired the power plant from Oklahoma Cogeneration LLC. In August 2019, OG&E received final approval from the APSC to acquire both plants. Further discussion can be found in Note 16. For the years ended December 31, 2019, 2018 and 2017, OG&E made total payments to cogenerators of $14.7 million, $112.4 million and $115.2 million, respectively, of which $7.4 million, $60.0 million and $63.0 million, respectively, represented capacity payments. All payments for purchased power, including cogeneration, are included in the Consolidated Statements of Income as Cost of Sales. Purchase Obligations and Commitments The Company's future purchase obligations and commitments estimated for the next five years are as follows: (In millions) 2020 2021 2022 2023 2024 Total Purchase obligations and commitments: Minimum purchase commitments $ 82.6 $ 55.1 $ 50.4 $ 50.4 $ 32.9 $ 271.4 Expected wind purchase commitments 55.7 56.0 56.4 56.8 57.5 282.4 Long-term service agreement commitments 2.4 2.4 2.4 13.8 32.1 53.1 Environmental compliance plan expenditures 0.4 — — — — 0.4 Total purchase obligations and commitments $ 141.1 $ 113.5 $ 109.2 $ 121.0 $ 122.5 $ 607.3 OG&E Minimum Purchase Commitments OG&E has coal contracts for purchases through June 30, 2020 and May 31, 2021, whereby OG&E has the right but not the obligation to purchase a defined quantity of coal. OG&E purchases its coal through spot purchases on an as-needed basis. As a participant in the SPP Integrated Marketplace, OG&E purchases its natural gas supply through short-term agreements. OG&E relies on a combination of natural gas base load agreements and call agreements, whereby OG&E has the right but not the obligation to purchase a defined quantity of natural gas, combined with day and intra-day purchases to meet the demands of the SPP Integrated Marketplace. OG&E has natural gas transportation service contracts with Enable and ONEOK, Inc. The contract with Enable ends in May 2024, and the contract with ONEOK, Inc. ends in August 2037. These transportation contracts grant Enable and ONEOK, Inc. the responsibility of delivering natural gas to OG&E's generating facilities. OG&E Wind Purchase Commitments The following table summarizes OG&E's wind power purchase contracts. Company Location Original Term of Contract Expiration of Contract MWs CPV Keenan Woodward County, OK 20 years 2030 152.0 Edison Mission Energy Dewey County, OK 20 years 2031 130.0 NextEra Energy Blackwell, OK 20 years 2032 60.0 The following table summarizes OG&E's wind power purchases for the years ended December 31, 2019, 2018 and 2017. Year Ended December 31 (In millions) 2019 2018 2017 CPV Keenan $ 27.2 $ 27.0 $ 29.0 Edison Mission Energy 23.1 21.7 22.1 NextEra Energy 7.4 6.8 7.4 FPL Energy (A) — 2.1 2.6 Total wind power purchased $ 57.7 $ 57.6 $ 61.1 (A) OG&E's purchased power contract with FPL Energy for 50 MWs expired in 2018. OG&E Long-Term Service Agreement Commitments OG&E has a long-term parts and service maintenance contract for the upkeep of the McClain Plant. In May 2013, a new contract was signed that is expected to run for the earlier of 128,000 factored-fired hours or 4,800 factored-fired starts. In December 2015, the McClain Long-Term Service Agreement was amended to define the terms and conditions for the exchange of spare rotors between OG&E and General Electric International, Inc. Based on historical usage and current expectations for future usage, this contract is expected to run until 2033. The contract requires payments based on both a fixed and variable cost component, depending on how much the McClain Plant is used. OG&E has a long-term parts and service maintenance contract for the upkeep of the Redbud Plant. In March 2013, the contract was amended to extend the contract coverage for an additional 24,000 factored-fired hours resulting in a maximum of the earlier of 144,000 factored-fired hours or 4,500 factored-fired starts. Based on historical usage and current expectations for future usage, this contract is expected to run until 2030. The contract requires payments based on both a fixed and variable cost component, depending on how much the Redbud Plant is used. Environmental Laws and Regulations The activities of the Company are subject to numerous stringent and complex federal, state and local laws and regulations governing environmental protection. These laws and regulations can change, restrict or otherwise impact the Company's business activities in many ways, including the handling or disposal of waste material, planning for future construction activities to avoid or mitigate harm to threatened or endangered species and requiring the installation and operation of emissions or pollution control equipment. Failure to comply with these laws and regulations could result in the assessment of administrative, civil and criminal penalties, the imposition of remedial requirements and the issuance of orders enjoining future operations. Management believes that all of its operations are in substantial compliance with current federal, state and local environmental standards. Environmental regulation can increase the cost of planning, design, initial installation and operation of OG&E's facilities. Management continues to evaluate its compliance with existing and proposed environmental legislation and regulations and implement appropriate environmental programs in a competitive market. Affordable Clean Energy Rule On July 8, 2019, the EPA published the Affordable Clean Energy rule. Numerous parties, not including OG&E, have filed petitions for judicial review of the Affordable Clean Energy rule in the U.S. Court of Appeals for the District of Columbia Circuit. The Affordable Clean Energy rule requires states, including Oklahoma, to develop emission limitations for carbon dioxide for each existing coal-fired utility boiler within the state, including all of OG&E's coal units, and submit a compliance and implementation plan to the EPA by July 2022. The EPA will approve or disapprove the proposed state plan within 18 months of submittal and develop a federal implementation plan if the proposed state plan is disapproved. The ultimate timing and impact of these standards on OG&E's operations cannot be determined with certainty at this time, although a requirement for significant reduction of CO 2 emissions from existing fossil-fuel-fired power plants ultimately could result in significant additional compliance costs that would affect the Company's future consolidated financial position, results of operations and cash flows if such costs are not recovered through regulated rates. Other

Rate Matters and Regulation

Rate Matters and Regulation	12 Months Ended
	Dec. 31, 2019
Regulated Operations [Abstract]
Rate Matters and Regulation	Rate Matters and Regulation Regulation and Rates OG&E's retail electric tariffs are regulated by the OCC in Oklahoma and by the APSC in Arkansas. The issuance of certain securities by OG&E is also regulated by the OCC and the APSC. OG&E's transmission activities, short-term borrowing authorization and accounting practices are subject to the jurisdiction of the FERC. The Secretary of the U.S. Department of Energy has jurisdiction over some of OG&E's facilities and operations. In 2019, 86 percent of OG&E's electric revenue was subject to the jurisdiction of the OCC, eight percent to the APSC and six percent to the FERC. The OCC and the APSC require that, among other things, (i) the Company permits the OCC and the APSC access to the books and records of the Company and its affiliates relating to transactions with OG&E; (ii) the Company employ accounting and other procedures and controls to protect against subsidization of non-utility activities by OG&E's customers; and (iii) the Company refrain from pledging OG&E assets or income for affiliate transactions. In addition, the FERC has access to the books and records of the Company and its affiliates as the FERC deems relevant to costs incurred by OG&E or necessary or appropriate for the protection of utility customers with respect to the FERC jurisdictional rates. Completed Regulatory Matters Arkansas 2018 Formula Rate Plan Filing Per OG&E's settlement in its last general rate review, OG&E filed an evaluation report under its Formula Rate Plan in October 2018. On March 6, 2019, the APSC approved a settlement agreement for a $3.3 million revenue increase, and new rates were effective as of April 1, 2019. Approval for Acquisition of Existing Power Plants In December 2018, OG&E filed an application for pre-approval from the OCC to acquire a 360 MW capacity coal- and natural gas-fired plant from AES and a 146 MW capacity natural gas-fired combined-cycle plant from Oklahoma Cogeneration LLC for $53.5 million. The purchase of these assets replaces capacity provided by purchased power contracts that expired in 2019 and helps OG&E satisfy its customers' energy needs and load obligations to the SPP. In addition, the filing sought approval of a rider mechanism to collect costs associated with the purchase of these generating facilities. On May 13, 2019, the OCC approved OG&E's acquisition of both plants, the requested rider mechanism for the AES plant and regulatory asset treatment for the Oklahoma Cogeneration LLC plant that will defer non-fuel operation and maintenance expenses, depreciation and ad valorem taxes. On January 23, 2019, OG&E filed an application for Federal Power Act Section 203 approval with a request for expedited consideration. This application requested FERC's prior authorization to acquire the AES and Oklahoma Cogeneration LLC plants. On May 22, 2019, OG&E received authorization from the FERC to acquire both plants. On April 24, 2019, OG&E filed an application with the APSC requesting approval of the acquisition, as well as depreciation rates, of the AES and Oklahoma Cogeneration LLC plants, and on May 8, 2019, OG&E received conditional approval for the purchase of the generating facilities. On August 30, 2019, the APSC issued an order finding that the plants to be acquired were used and useful and that the acquisition of the plants was in the public interest. The APSC also approved the depreciation rates to be applied to the acquired plants. The cost OG&E paid for the acquired plants was reviewed by the APSC in OG&E's 2019 Formula Rate Plan filing, and parties reached a settlement agreement requesting the APSC to approve the cost of the acquisitions. OG&E is awaiting a final decision from the APSC. In May 2019, OG&E completed the acquisition of the power plant from AES and placed it into service, which is now named the River Valley power plant. In August 2019, OG&E completed the acquisition of the power plant from Oklahoma Cogeneration LLC and placed it into service, which is now named the Frontier power plant. Fuel Adjustment Clause Review for Calendar Year 2017 In July 2018, the OCC staff filed an application to review OG&E's fuel adjustment clause for the calendar year 2017, including the prudence of OG&E's electric generation, purchased power and fuel procurement costs. On February 1, 2019, the Administrative Law Judge recommended that OG&E's processes, costs, investments and decisions regarding fuel procurement for the 2017 calendar year be found prudent. On May 22, 2019, the OCC deemed OG&E's electric generation, purchased power and fuel procurement costs to be materially prudent. Oklahoma Rate Review Filing - December 2018 In December 2018, OG&E filed a general rate review with the OCC, requesting a rate increase of $77.6 million per year to recover its investment in the Dry Scrubbers project and in the conversion of Muskogee Units 4 and 5 to natural gas, to align OG&E's return on equity more closely to the industry average and to align OG&E's depreciation rates to more realistically reflect its assets' lifespans. On May 24, 2019, OG&E entered into a non-unanimous joint stipulation and settlement agreement with the OCC staff, the Attorney General's Office of Oklahoma, the Oklahoma Industrial Energy Consumers and certain other parties associated with the requested rate increase. The filing was further amended on May 30, 2019 to include Oklahoma Association of Electric Cooperatives as a settling party. Under the terms of the settlement agreement, OG&E would receive full recovery of its environmental investments in the Dry Scrubbers project and in the conversion of Muskogee Units 4 and 5 to natural gas. Base rates would not change as a result of the settlement agreement due to the reduction of costs related to cogeneration contracts and the acceleration of unprotected deferred tax savings over a 10-year period. Further, OG&E's current depreciation rates and return on equity of 9.5 percent for purposes of calculating the allowance for funds used during construction and OG&E's various recovery riders that include a full return component would remain unchanged. On July 1, 2019, OG&E implemented interim rates, which were subject to refund of any amount recovered in excess of the rates ultimately approved by the OCC in the rate review. On September 19, 2019, the OCC issued a final order which approved the settlement agreement. The Dry Scrubbers project, which includes the installation of two dry scrubbers at the Sooner plant, and the conversion of Muskogee Units 4 and 5 to natural gas were initiated in response to the EPA's MATS and Regional Haze Rule FIP. The Dry Scrubber systems on Sooner Unit 1 and Unit 2 were placed into service in October 2018 and January 2019, respectively. Muskogee Units 4 and 5 were placed into service in March 2019. Fuel Adjustment Clause Review for Calendar Year 2018 In June 2019, the OCC staff filed an application to review OG&E's fuel adjustment clause for the calendar year 2018, including the prudence of OG&E's electric generation, purchased power and fuel procurement costs. On December 12, 2019, the OCC issued an order deeming OG&E's electric generation, purchased power and fuel procurement costs were prudent. FERC - Section 206 Filing In January 2018, the Oklahoma Municipal Power Authority filed a complaint at the FERC stating that the base return on common equity used by OG&E in calculating formula transmission rates under the SPP Open Access Transmission Tariff is unjust and unreasonable and should be reduced from 10.60 percent to 7.85 percent, effective upon the date of the complaint. In addition to the request to reduce the return on equity, the Oklahoma Municipal Power Authority's complaint also requests that modifications be made to OG&E's transmission formula rates to reflect the impacts of the 2017 Tax Act, including the 2017 Tax Act's impact on accumulated deferred income tax balances. In May 2019, all parties agreed to a settlement which provides for 10 percent base return on equity, plus a 50-basis point adder, and a five-year amortization period of the unprotected excess accumulated deferred income taxes associated with the 2017 Tax Act. On November 21, 2019, the FERC approved the settlement agreement. Pending Regulatory Matters Set forth below is a list of various proceedings pending before state or federal regulatory agencies. Unless stated otherwise, OG&E cannot predict when the regulatory agency will act or what action the regulatory agency will take. OG&E's financial results are dependent in part on timely and adequate decisions by the regulatory agencies that set OG&E's rates. FERC Order for Sponsored Transmission Upgrades within SPP Under the SPP Open Access Transmission Tariff, costs of participant-funded, or "sponsored," transmission upgrades may be recovered from other SPP customers whose transmission service depends on capacity enabled by the upgrade. The SPP Open Access Transmission Tariff required SPP to charge for these upgrades beginning in 2008, but SPP had not been charging its customers for these upgrades due to information system limitations. However, SPP had informed participants in the market that these charges would be forthcoming. In July 2016, the FERC granted SPP's request to recover the charges not billed since 2008. SPP subsequently billed OG&E for these charges and credited OG&E related to transmission upgrades that OG&E had sponsored, which resulted in OG&E being a net receiver of sponsored upgrade credits. The majority of these net credits were refunded to customers through OG&E's various rate riders that include SPP activity with the remaining amounts retained by OG&E. Several companies that were net payers of Z2 charges sought rehearing of the FERC's July 2016 order; however, in November 2017, the FERC denied the rehearing requests. In January 2018, one of the impacted companies appealed the FERC's decision to the U.S. Court of Appeals for the District of Columbia Circuit. In July 2018, that court granted a motion requested by the FERC that the case be remanded back to the FERC for further examination and proceedings. In February 2019, the FERC reversed its July 2016 order and November 2017 rehearing denial, ruled that SPP violated its tariff to charge for the 2008 - 2015 period in 2016, held that the SPP tariff provision that prohibited those charges could not be waived and ordered SPP to develop a plan to refund the payments but not to implement the refunds until further ordered to do so. In response, on April 1, 2019, OG&E filed a request for rehearing with the FERC, and on May 24, 2019, OG&E filed a FERC 206 complaint against SPP, alleging that SPP's forced unwinding of the revenue credit payments to OG&E would violate the provisions of the Sponsored Upgrade Agreement and of the applicable tariff. OG&E's filing requested that the FERC rule that SPP is not entitled to seek refunds or in any other way seek to unwind the revenue credit payments it had paid to OG&E pursuant to the Sponsored Upgrade Agreement. SPP's response to OG&E's filing agreed that OG&E should be entitled to keep its Z2 payments and argued that SPP should not be held responsible for those payments if refunds are ordered. Further, SPP has requested the FERC to negotiate a global settlement with all impacted parties, including other project sponsors who, like OG&E, have also filed complaints at FERC contending that the payments they have received cannot properly be unwound. On February 20, 2020, the FERC denied OG&E's request for rehearing of its February 28, 2019 order, denying the waiver and ruling that SPP must seek refunds from project sponsors for Z2 payments for the 2008 - 2015 period and pay them back to transmission owners. The FERC also denied SPP's request for a stay and for institution of settlement procedures. The FERC stated it would not institute settlement procedures unless parties on both sides of the matter requested them. The FERC did not rule on OG&E's complaint or the complaints of other project sponsors, or consider SPP's refund plan. The FERC thus has not set any date for payment of refunds. The FERC's order denying the waiver and requiring refunds is now appealable, and OG&E intends to file a timely appeal. The Company cannot predict the outcome of this proceeding based on currently available information, and as of December 31, 2019 and at present time, the Company has not reserved an amount for a potential refund. If the reversal of the July 2016 FERC order remains intact, OG&E estimates it would be required to refund $13.0 million, which is net of amounts paid to other utilities for upgrades and would be subject to interest at the FERC-approved rate. If refunds were required, recovery of these upgrade credits would shift to future periods. Of the $13.0 million, the Company would be impacted by $5.0 million in expense that initially benefited the Company in 2016, and OG&E customers would incur a net impact of $8.0 million in expense through rider mechanisms or the FERC formula rate. SPP has recently proposed eliminating Attachment Z2 revenue crediting and replacing it with a different mechanism that would provide project sponsors such as OG&E the same level of recovery they would receive if payments continued under Attachment Z2. The FERC rejected that proposal to the extent it would limit recovery to the amount of the upgrade sponsor's directly assigned upgrade costs with interest, finding that providing the possibility of recovering greater than the cost of the investment could serve as an incentive for entities to build merchant transmission projects. The SPP can resubmit a proposal without that cap. APSC - Environmental Compliance Plan Rider On May 31, 2019, OG&E filed an environmental compliance plan rider in Arkansas to recover its investment for the environmentally mandated costs associated with the Dry Scrubbers project and the conversion of Muskogee Units 4 and 5 to natural gas. The filing is an interim surcharge, subject to refund, that began with the first billing cycle of June 2019. OG&E is reserving the amounts collected through the interim surcharge, pending APSC approval of OG&E's filing. A hearing on the merits was held on December 17, 2019. The primary question before the APSC is whether a company can utilize an environmental compliance plan rider while also regulated under a formula rate plan. OG&E is awaiting a final decision from the APSC. Arkansas 2019 Formula Rate Plan Filing OG&E filed its second evaluation report under its Formula Rate Plan in October 2019. On January 29, 2020, OG&E, the General Staff of the APSC and the Office of the Arkansas Attorney General filed a settlement agreement requesting the APSC approve a $5.2 million revenue increase, with rates effective April 1, 2020. The settling parties agreed that the Series I grid modernization projects are prudent in both action and cost and that the Series II grid modernization projects are prudent in action only and the determination of prudence of costs will be reserved until the actual historical costs are reviewed. The settling parties also agreed that OG&E will no longer use projections for the remaining initial term or extension of its current Formula Rate Plan and that all costs will be included for recovery for the first time in the historical year. A hearing was held on February 5, 2020, and OG&E is awaiting a final decision from the APSC. Oklahoma Grid Enhancement Plan On February 24, 2020, OG&E filed an application with the OCC for approval of a mechanism that allows for interim recovery of the costs associated with its grid enhancement plan. The plan includes approximately $800 million of strategic, data-driven investments, over five years, covering grid resiliency, grid automation, communication systems and technology platforms and applications. A procedural schedule has not been set by the OCC. Oklahoma Retail Electric Supplier Certified Territory Act Causes

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Data [Abstract]
Quarterly Financial Information [Text Block]	Quarterly Financial Data (Unaudited) Due to the seasonal fluctuations and other factors of the Company's businesses, the operating results for interim periods are not necessarily indicative of the results that may be expected for the year. In the Company's opinion, the following quarterly financial data includes all adjustments, consisting of normal recurring adjustments, necessary to fairly present such amounts. Summarized consolidated quarterly unaudited financial data is as follows: Quarter Ended ( In millions, except per share data) March 31 June 30 September 30 December 31 Total Operating revenues 2019 $ 490.0 $ 513.7 $ 755.4 $ 472.5 $ 2,231.6 2018 $ 492.7 $ 567.0 $ 698.8 $ 511.8 $ 2,270.3 Operating income 2019 $ 49.7 $ 110.0 $ 274.3 $ 70.3 $ 504.3 2018 $ 66.6 $ 137.7 $ 227.3 $ 58.0 $ 489.6 Net income 2019 $ 47.1 $ 100.2 $ 250.9 $ 35.4 $ 433.6 2018 $ 55.0 $ 110.7 $ 205.1 $ 54.7 $ 425.5 Basic earnings per average common share (A) 2019 $ 0.24 $ 0.50 $ 1.25 $ 0.18 $ 2.17 2018 $ 0.28 $ 0.55 $ 1.03 $ 0.27 $ 2.13 Diluted earnings per average common share (A) 2019 $ 0.24 $ 0.50 $ 1.25 $ 0.18 $ 2.16 2018 $ 0.27 $ 0.55 $ 1.02 $ 0.27 $ 2.12

Schedule II

Schedule II	9 Months Ended
	Sep. 30, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	SCHEDULE II - Valuation and Qualifying Accounts Additions Description Balance at Beginning of Period Charged to Costs and Expenses Deductions (A) Balance at End of Period (In millions) Balance at December 31, 2017 Reserve for Uncollectible Accounts $ 1.5 $ 2.6 $ 2.6 $ 1.5 Balance at December 31, 2018 Reserve for Uncollectible Accounts $ 1.5 $ 3.4 $ 3.2 $ 1.7 Balance at December 31, 2019 Reserve for Uncollectible Accounts $ 1.7 $ 2.2 $ 2.4 $ 1.5

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidation, Policy [Policy Text Block]	Organization The Company is a holding company with investments in energy and energy services providers offering physical delivery and related services for both electricity and natural gas primarily in the south central U.S. The Company conducts these activities through two business segments: (i) electric utility and (ii) natural gas midstream operations. The accounts of the Company and its wholly-owned subsidiaries are included in the Consolidated Financial Statements. All intercompany transactions and balances are eliminated in consolidation. The Company generally uses the equity method of accounting for investments where its ownership interest is between 20 percent and 50 percent and it lacks the power to direct activities that most significantly impact economic performance. The electric utility segment generates, transmits, distributes and sells electric energy in Oklahoma and western Arkansas. Its operations are conducted through OG&E and are subject to regulation by the OCC, the APSC and the FERC. OG&E was incorporated in 1902 under the laws of the Oklahoma Territory and is a wholly-owned subsidiary of the Company. OG&E is the largest electric utility in Oklahoma, and its franchised service territory includes Fort Smith, Arkansas and the surrounding communities. OG&E sold its retail natural gas business in 1928 and is no longer engaged in the natural gas distribution business. The natural gas midstream operations segment represents the Company's investment in Enable through wholly-owned subsidiaries and ultimately OGE Holdings. Enable is primarily engaged in the business of gathering, processing, transporting and storing natural gas. Enable's natural gas gathering and processing assets are strategically located in four states and serve natural gas production in the Anadarko, Arkoma and Ark-La-Tex Basins. Enable also owns crude oil gathering assets in the Anadarko and Williston Basins. Enable has intrastate natural gas transportation and storage assets that are located in Oklahoma as well as interstate assets that extend from western Oklahoma and the Texas Panhandle to Louisiana, from Louisiana to Illinois and from Louisiana to Alabama. Enable's general partner is equally controlled by the Company and CenterPoint, who each have 50 percent management ownership. Based on the 50/50 management ownership, with neither company having control, the Company accounts for its interest in Enable using the equity method of accounting.
Public Utilities, Policy [Policy Text Block]	Accounting Records The accounting records of OG&E are maintained in accordance with the Uniform System of Accounts prescribed by the FERC and adopted by the OCC and the APSC. Additionally, OG&E, as a regulated utility, is subject to accounting principles for certain types of rate-regulated activities, which provide that certain incurred costs that would otherwise be charged to expense can be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense can be deferred as regulatory liabilities, based on the expected flowback to customers in future rates. Management's expected recovery of deferred costs and flowback of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. OG&E records certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refund in future rates.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents
Allowance for Uncollectible Accounts Receivable, Policy	Customer balances are generally written off if not collected within six months after the final billing date. The allowance for uncollectible accounts receivable for OG&E is calculated by multiplying the last six months of electric revenue by the provision rate, which is based on a 12-month historical average of actual balances written off. To the extent the historical collection rates are not representative of future collections, there could be an effect on the amount of uncollectible expense recognized. Also, a portion of the uncollectible provision related to fuel within the Oklahoma jurisdiction is being recovered through the fuel adjustment clause. The allowance for uncollectible accounts receivable is a reduction to Accounts Receivable in the Consolidated Balance Sheets and is included in Other Operation and Maintenance Expense in the Consolidated Statements of Income. The allowance for uncollectible accounts receivable was $1.5 million and $1.7 million at December 31, 2019 and 2018, respectively.
Inventory, Policy [Policy Text Block]	Fuel Inventories Fuel inventories for the generation of electricity consist of coal, natural gas and oil. OG&E uses the weighted-average cost method of accounting for inventory that is physically added to or withdrawn from storage or stockpiles. The amount of fuel inventory was $46.3 million and $57.6 million at December 31, 2019 and 2018, respectively.
Property, Plant and Equipment, Policy [Policy Text Block]	Property, Plant and Equipment
Depreciation and Amortization, Policy [Policy Text Block]	Depreciation and Amortization The provision for depreciation, which was 2.7 percent of the average depreciable utility plant for both 2019 and 2018, is calculated using the straight-line method over the estimated service life of the utility assets. Depreciation is provided at the unit level for production plant and at the account or sub-account level for all other plant and is based on the average life group method. In 2020, the provision for depreciation is projected to be 2.7 percent of the average depreciable utility plant. Amortization of intangible assets is calculated using the straight-line method. Of the remaining amortizable intangible plant balance at December 31, 2019, 98.9 percent will be amortized over 10.4 years with the remaining 1.1 percent of the intangible plant balance at December 31, 2019 being amortized over 23.7 years. Amortization of plant acquisition adjustments is provided on a straight-line basis over the estimated remaining service life of the acquired assets. Plant acquisition adjustments include $148.3 million for the Redbud Plant, which is being amortized over a 27 year life and $3.3 million for certain transmission substation facilities in OG&E's service territory, which are being amortized over a 37 to 59 year period.
Equity Method Investments [Policy Text Block]	Investment in Unconsolidated Affiliates The Company's investment in Enable is considered to be a variable interest entity because the owners of the equity at risk in this entity have disproportionate voting rights in relation to their obligations to absorb the entity's expected losses or to receive its expected residual returns. However, the Company is not considered the primary beneficiary of Enable since it does not have the power to direct the activities of Enable that are considered most significant to the economic performance of Enable; therefore, the Company accounts for its investment in Enable using the equity method of accounting. Under the equity method, the investment will be adjusted each period for contributions made, distributions received and the Company's share of the investee's comprehensive income as adjusted for basis differences. The Company's maximum exposure to loss related to Enable is limited to the Company's equity investment in Enable at December 31, 2019 as presented in Note 14. The Company evaluates its equity method investments for impairment when events or changes in circumstances indicate there is a loss in value of the investment that is other than a temporary decline. The Company considers distributions received from Enable which do not exceed cumulative equity in earnings subsequent to the date of investment to be a return on investment and are classified as operating activities in the Consolidated Statements of Cash Flows. The Company considers distributions received from Enable in excess of cumulative equity in earnings subsequent to the date of investment to be a return of investment and are classified as investing activities in the Consolidated Statements of Cash Flows.
Asset Retirement Obligation [Policy Text Block]	Asset Retirement ObligationsOG&E has asset retirement obligations primarily associated with the removal of company-owned wind turbines on leased land, as well as the removal of asbestos from certain power generating stations. The Company has recorded asset retirement obligations that are being accreted over their respective lives ranging from ten to 68 years.
Allowance for Funds Used During Construction, Policy [Policy Text Block]	Allowance for Funds Used During Construction
Collection of Sales Tax, Policy [Policy Text Block]	Collection of Sales Tax
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition General OG&E recognizes revenue from electric sales when power is delivered to customers. The performance obligation to deliver electricity is generally created and satisfied simultaneously, and the provisions of the regulatory-approved tariff determine the charges OG&E may bill the customer, payment due date and other pertinent rights and obligations of both parties. OG&E reads its customers' meters and sends bills to its customers throughout each month. As a result, there is a significant amount of customers' electricity consumption that has not been billed at the end of each month. OG&E accrues an estimate of the revenues for electric sales delivered since the latest billings. Unbilled revenue is presented in Accrued Unbilled Revenues in the Consolidated Balance Sheets and in Revenues from Contracts with Customers in the Consolidated Statements of Income based on estimates of usage and prices during the period. The estimates that management uses in this calculation could vary from the actual amounts to be paid by customers. Integrated Market and Transmission OG&E currently owns and operates transmission and generation facilities as part of a vertically integrated utility. OG&E is a member of the SPP regional transmission organization and has transferred operational authority, but not ownership, of OG&E's transmission facilities to the SPP. The SPP has implemented FERC-approved regional day-ahead and real-time markets for energy and operating services, as well as associated transmission congestion rights. Collectively the three markets operate together under the global name, SPP Integrated Marketplace. OG&E represents owned and contracted generation assets and customer load in the SPP Integrated Marketplace for the sole benefit of its customers. OG&E has not participated in the SPP Integrated Marketplace for any speculative trading activities. OG&E records the SPP Integrated Marketplace transactions as sales or purchases per FERC Order 668, which requires that purchases and sales be recorded on a net basis for each settlement period of the SPP Integrated Marketplace. Purchases and sales are based on the fixed transaction price determined by the market at the time of the purchase or sale and the MWh quantity purchased or sold. These results are reported as Revenues from Contracts with Customers or Cost of Sales in the Consolidated Financial Statements. OG&E revenues, expenses, assets and liabilities may be adversely affected by changes in the organization, operating and regulation by the FERC or the SPP. OG&E's transmission revenues are generated by the use of OG&E's transmission network by the SPP, which operates the network, on behalf of other transmission owners. OG&E recognizes revenue on the sale of transmission service to its customers over time as the service is provided in the amount OG&E has a right to invoice. Transmission service to the SPP is billed monthly based on a fixed transaction price determined by OG&E's FERC-approved formula transmission rates along with other SPP-specific charges and the megawatt quantity reserved. Other Revenues Revenues from Alternative Revenue Programs
Fuel Adjustment Clauses, Policy [Policy Text Block]	Fuel Adjustment Clauses The actual cost of fuel used in electric generation and certain purchased power costs are passed through to OG&E's customers through fuel adjustment clauses. The fuel adjustment clauses are subject to periodic review by the OCC and the APSC.
Lessee, Leases	LeasesThe Company evaluates all contracts under ASC 842 to determine if the contract is or contains a lease and to determine classification as an operating or finance lease. If a lease is identified, the Company recognizes a right-of-use asset and a lease liability in its Consolidated Balance Sheets. The Company recognizes and measures a lease liability when it concludes the contract contains an identified asset that the Company controls through having the right to obtain substantially all of the economic benefits and the right to direct the use of the identified asset. The liability is equal to the present value of lease payments, and the asset is based on the liability, subject to adjustment, such as for initial direct costs. Further, the Company utilizes an incremental borrowing rate for purposes of measuring lease liabilities, if the discount rate is not implicit in the lease. To calculate the incremental borrowing rate, the Company starts with a current pricing report for the Company's senior unsecured notes, which indicates rates for periods reflective of the lease term, and adjusts for the effects of collateral to arrive at the secured incremental borrowing rate. As permitted by ASC 842, the Company made an accounting policy election to not apply the balance sheet recognition requirements to short-term leases and to not separate lease components from nonlease components when recognizing and measuring lease liabilities. For income statement purposes, the Company records operating lease expense on a straight-line basis.
Income Taxes, Policy [Policy Text Block]	Income Taxes The Company files consolidated income tax returns in the U.S. federal jurisdiction and various state jurisdictions. Income taxes are generally allocated to each company in the affiliated group based on its stand-alone taxable income or loss. Federal investment tax credits previously claimed on electric utility property have been deferred and will be amortized to income over the life of the related property. The Company uses the asset and liability method of accounting for income taxes. Under this method, a deferred tax asset or liability is recognized for the estimated future tax effects attributable to temporary differences between the financial statement basis and the tax basis of assets and liabilities as well as tax credit carry forwards and net operating loss carry forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period of the change. The Company recognizes interest related to unrecognized tax benefits in Interest Expense and recognizes penalties in Other Expense in the Consolidated Statements of Income.
Accrued Vacation, Policy [Policy Text Block]	Accrued Vacation The Company accrues vacation pay monthly by establishing a liability for vacation earned. Vacation may be taken as earned and is charged against the liability. At the end of each year, the liability represents the amount of vacation earned but not taken.
Environmental Costs, Policy [Policy Text Block]	Accruals for environmental costs are recognized when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are charged to expense or deferred as a regulatory asset based on expected recovery from customers in future rates, if they relate to the remediation of conditions caused by past operations or if they are not expected to mitigate or prevent contamination from future operations. Where environmental expenditures relate to facilities currently in use, such as pollution control equipment, the costs may be capitalized and depreciated over the future service periods. Estimated remediation costs are recorded at undiscounted amounts, independent of any insurance or rate recovery, based on prior experience, assessments and current technology. Accrued obligations are regularly adjusted as environmental assessments and estimates are revised and remediation efforts proceed. For sites where OG&E has been designated as one of several potentially responsible parties, the amount accrued represents OG&E's estimated share of the cost. The Company had $18.7 million and $23.4 million in accrued environmental liabilities at December 31, 2019 and 2018, respectively, which are included in the Company's asset retirement obligations.
Fair Value of Financial Instruments, Policy [Policy Text Block]	Fair Value Measurements The classification of the Company's fair value measurements requires judgment regarding the degree to which market data is observable or corroborated by observable market data. GAAP establishes a fair value hierarchy that prioritizes the inputs used to measure fair value based on observable and unobservable data. The hierarchy categorizes the inputs into three levels, with the highest priority given to quoted prices in active markets for identical unrestricted assets or liabilities (Level 1) and the lowest priority given to unobservable inputs (Level 3). Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The three levels defined in the fair value hierarchy are as follows: Level 1 inputs are quoted prices in active markets for identical unrestricted assets or liabilities that are accessible at the measurement date. Level 2 inputs are inputs other than quoted prices in active markets included within Level 1 that are either directly or indirectly observable at the reporting date for the asset or liability for substantially the full term of the asset or liability. Level 2 inputs include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. Level 3 inputs are prices or valuation techniques for the asset or liability that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). Unobservable inputs reflect the reporting entity's own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk).
Share-based Compensation, Option and Incentive Plans, Policy [Policy Text Block]	Performance Units Under the Stock Incentive Plan, the Company has issued performance units which represent the value of one share of the Company's common stock. The performance units provide for accelerated vesting if there is a change in control (as defined in the Stock Incentive Plan). Each performance unit is subject to forfeiture if the recipient terminates employment with the Company or a subsidiary prior to the end of the primarily three-year award cycle for any reason other than death, disability or retirement. In the event of death, disability or retirement, a participant will receive a prorated payment based on such participant's number of full months of service during the award cycle, further adjusted based on the achievement of the performance goals during the award cycle. The Company estimates expected forfeitures in accounting for performance unit compensation expense. The performance units granted based on total shareholder return are contingently awarded and will be payable in shares of the Company's common stock subject to the condition that the number of performance units, if any, earned by the employees upon the expiration of a primarily three-year award cycle (i.e., three-year cliff vesting period) is dependent on the Company's total shareholder return ranking relative to a peer group of companies. The performance units granted based on earnings per share are contingently awarded and will be payable in shares of the Company's common stock based on the Company's earnings per share growth over a primarily three-year award cycle (i.e., three-year cliff vesting period) compared to a target set at the time of the grant by the Compensation Committee of the Company's Board of Directors. All of these performance units are classified as equity in the Consolidated Balance Sheets. If there is no or only a partial payout for the performance units at the end of the award cycle, the unearned performance units are cancelled. Payout requires approval of the Compensation Committee of the Company's Board of Directors. Payouts, if any, are all made in common stock and are considered made when the payout is approved by the Compensation Committee. Performance Units – Total Shareholder Return Restricted Stock Units Under the Stock Incentive Plan, the Company has issued restricted stock units to certain existing non-officer employees as well as other executives upon hire to attract and retain individuals to be competitive in the marketplace, and for the 2019 grant cycle, restricted stock units were granted in lieu of performance units based on earnings per share. The restricted stock units vest primarily in a three-year award cycle (i.e., three-year cliff vesting period). Prior to vesting, each restricted stock unit is subject to forfeiture if the recipient ceases to render substantial services to the Company or a subsidiary. These restricted stock units may not be sold, assigned, transferred or pledged and are subject to a risk of forfeiture. The fair value of the restricted stock units was based on the closing market price of the Company's common stock on the grant date. Compensation expense for the restricted stock units is a fixed amount determined at the grant date fair value and is recognized as services are rendered by employees over a primarily three-year vesting period. Also, for those restricted stock units that vest in one-third annual increments over a three-year cycle, the Company treats its restricted stock units as multiple separate awards by recording compensation expense separately for each tranche whereby a substantial portion of the expense is recognized in the earlier years in the requisite service period.
Earnings Per Share, Policy [Policy Text Block]	Earnings Per Share
Pension and Other Postretirement Plans, Policy [Policy Text Block]	Pension Plan and Restoration of Retirement Income Plan It is the Company's policy to fund the Pension Plan on a current basis based on the net periodic pension expense as determined by the Company's actuarial consultants. Such contributions are intended to provide not only for benefits attributed to service to date but also for those expected to be earned in the future. The Company made a $20.0 million and $15.0 million contribution to its Pension Plan in 2019 and 2018, respectively. The Company has not determined whether it will need to make any contributions to the Pension Plan in 2020. Any contribution to the Pension Plan during 2020 would be a discretionary contribution, anticipated to be in the form of cash, and is not required to satisfy the minimum regulatory funding requirement specified by the Employee Retirement Income Security Act of 1974, as amended. The Company could be required to make additional contributions if the value of its pension trust and postretirement benefit plan trust assets are adversely impacted by a major market disruption in the future. Postretirement Benefit Plans In addition to providing pension benefits, the Company provides certain medical and life insurance benefits for eligible retired members. Regular, full-time, active employees hired prior to February 1, 2000 whose age and years of credited service total or exceed 80 or have attained at least age 55 with 10 or more years of service at the time of retirement are entitled to postretirement medical benefits, while employees hired on or after February 1, 2000 are not entitled to postretirement medical benefits. Eligible retirees must contribute such amount as the Company specifies from time to time toward the cost of coverage for postretirement benefits. The benefits are subject to deductibles, co-payment provisions and other limitations. OG&E charges postretirement benefit costs to expense and includes an annual amount as a component of the cost-of-service in future ratemaking proceedings.
Postemployment Benefit Plans, Policy [Policy Text Block]	Post-Employment Benefit Plan Disabled employees receiving benefits from the Company's Group Long-Term Disability Plan are entitled to continue participating in the Company's Medical Plan along with their dependents. The post-employment benefit obligation represents the actuarial present value of estimated future medical benefits that are attributed to employee service rendered prior to the date as of which such information is presented. The obligation also includes future medical benefits expected to be paid to current employees participating in the Company's Group Long-Term Disability Plan and their dependents, as defined in the Company's Medical Plan.
Plan Investments, Policies and Strategies, Policy [Policy Text Block]	Pension Plan Investments, Policies and Strategies The Pension Plan assets are held in a trust which follows an investment policy and strategy designed to reduce the funded status volatility of the Plan by utilizing liability driven investing. The purpose of liability-driven investing is to structure the asset portfolio to more closely resemble the pension liability and thereby more effectively hedge against changes in the liability. The investment policy follows a glide path approach that shifts a higher portfolio weighting to fixed income as the Plan's funded status increases. The table below sets forth the targeted fixed income and equity allocations at different funded status levels. Projected Benefit Obligation Funded Status Thresholds <90% 95% 100% 105% 110% 115% 120% Fixed income 50% 58% 65% 73% 80% 85% 90% Equity 50% 42% 35% 27% 20% 15% 10% Total 100% 100% 100% 100% 100% 100% 100% Within the portfolio's overall allocation to equities, the funds are allocated according to the guidelines in the table below. Asset Class Target Allocation Minimum Maximum Domestic Large Cap Equity 40% 35% 60% Domestic Mid-Cap Equity 15% 5% 25% Domestic Small-Cap Equity 25% 5% 30% International Equity 20% 10% 30% The Company has retained an investment consultant responsible for the general investment oversight, analysis, monitoring investment guideline compliance and providing quarterly reports to certain of the Company's members and the Company's Investment Committee. The various investment managers used by the trust operate within the general operating objectives as established in the investment policy and within the specific guidelines established for each investment manager's respective portfolio. The portfolio is rebalanced at least on an annual basis to bring the asset allocations of various managers in line with the target asset allocation listed above. More frequent rebalancing may occur if there are dramatic price movements in the financial markets which may cause the trust's exposure to any asset class to exceed or fall below the established allowable guidelines. To evaluate the progress of the portfolio, investment performance is reviewed quarterly. It is, however, expected that performance goals will be met over a full market cycle, normally defined as a three to five year period. Analysis of performance is within the context of the prevailing investment environment and the advisors' investment style. The goal of the trust is to provide a rate of return consistently from three percent to five percent over the rate of inflation (as measured by the national Consumer Price Index) on a fee adjusted basis over a typical market cycle of no less than three years and no more than five years. Each investment manager is expected to outperform its respective benchmark. Below is a list of each asset class utilized with appropriate comparative benchmark(s) each manager is evaluated against: Asset Class Comparative Benchmark(s) Active Duration Fixed Income Bloomberg Barclays Aggregate Long Duration Fixed Income Duration blended Barclays Long Government/Credit & Barclays Universal Equity Index Standard & Poor's 500 Index Mid-Cap Equity Russell Midcap Index Russell Midcap Value Index Small-Cap Equity Russell 2000 Index Russell 2000 Value Index International Equity Morgan Stanley Capital International ACWI ex-U.S. The fixed income managers are expected to use discretion over the asset mix of the trust assets in their efforts to maximize risk-adjusted performance. Exposure to any single issuer, other than the U.S. government, its agencies or its instrumentalities (which have no limits), is limited to five percent of the fixed income portfolio as measured by market value. At least 75 percent of the invested assets must possess an investment-grade rating at or above Baa3 or BBB- by Moody's Investors Service, S&P's Global Ratings or Fitch Ratings. The portfolio may invest up to 10 percent of the portfolio's market value in convertible bonds as long as the securities purchased meet the quality guidelines. A portfolio may invest up to 15 percent of the portfolio's market value in private placement, including 144A securities with or without registration rights and allow for futures to be traded in the portfolio. The purchase of any of the Company's equity, debt or other securities is prohibited. The domestic value equity managers focus on stocks that the manager believes are undervalued in price and earn an average or less than average return on assets and often pays out higher than average dividend payments. The domestic growth equity manager will invest primarily in growth companies which consistently experience above average growth in earnings and sales, earn a high return on assets and reinvest cash flow into existing business. The domestic mid-cap equity portfolio manager focuses on companies with market capitalizations lower than the average company traded on the public exchanges with the following characteristics: price/earnings ratio at or near the Russell Midcap Index, small dividend yield, return on equity at or near the Russell Midcap Index and an earnings per share growth rate at or near the Russell Midcap Index. The domestic small-cap equity manager will purchase shares of companies with market capitalizations lower than the average company traded on the public exchanges with the following characteristics: price/earnings ratio at or near the Russell 2000, small dividend yield, return on equity at or near the Russell 2000 and an earnings per share growth rate at or near the Russell 2000. The international global equity manager invests primarily in non-dollar denominated equity securities. Investing internationally diversifies the overall trust across the global equity markets. The manager is required to operate under certain restrictions including regional constraints, diversification requirements and percentage of U.S. securities. The Morgan Stanley Capital International All Country World ex-U.S. Index is the benchmark for comparative performance purposes. The Morgan Stanley Capital International All Country World ex-U.S. Index is a market value weighted index designed to measure the combined equity market performance of developed and emerging markets countries, excluding the U.S. All of the equities which are purchased for the international portfolio are thoroughly researched. All securities are freely traded on a recognized stock exchange, and there are no over-the-counter derivatives. The following investment categories are excluded: options (other than traded currency options), commodities, futures (other than currency futures or currency hedging), short sales/margin purchases, private placements, unlisted securities and real estate (but not real estate shares).
Pension and Other Postretirement Plans, Nonpension Benefits, Policy [Policy Text Block]	401(k) Plan The Company provides a 401(k) Plan, and each regular full-time employee of the Company or a participating affiliate is eligible to participate in the 401(k) Plan immediately. All other employees of the Company or a participating affiliate are eligible to become participants in the 401(k) Plan after completing one year of service as defined in the 401(k) Plan. Participants may contribute each pay period any whole percentage between two percent and 19 percent of their compensation, as defined in the 401(k) Plan, for that pay period. Participants who have reached age 50 before the close of a year are allowed to make additional contributions referred to as "Catch-Up Contributions," subject to certain limitations of the Code. Participants may designate, at their discretion, all or any portion of their contributions as: (i) a before-tax contribution under Section 401(k) of the Code subject to the limitations thereof, (ii) a contribution made on a non-Roth after-tax basis or (iii) a Roth contribution. The 401(k) Plan also includes an eligible automatic contribution arrangement and provides for a qualified default investment alternative consistent with the U.S. Department of Labor regulations. Participants may elect, in accordance with the 401(k) Plan procedures, to have their future salary deferral rate to be automatically increased annually on a date and in an amount as specified by the participant in such election. For employees hired or rehired on or after December 1, 2009, the Company contributes to the 401(k) Plan, on behalf of each participant, 200 percent of the participant's contributions up to five percent of compensation. No Company contributions are made with respect to a participant's Catch-Up Contributions, rollover contributions or with respect to a participant's contributions based on overtime payments, pay-in-lieu of overtime for exempt personnel, special lump-sum recognition awards and lump-sum merit awards included in compensation for determining the amount of participant contributions. Once made, the Company's contribution may be directed to any available investment option in the 401(k) Plan. The Company match contributions vest over a three-year period. After two years of service, participants become 20 percent vested in their Company contribution account and become fully vested on completing three years of service. In addition, participants fully vest when they are eligible for normal or early retirement under the Pension Plan requirements, in the event of their termination due to death or permanent disability or upon attainment of age 65 while employed by the Company or its affiliates. The Company contributed $14.4 million, $13.2 million and $13.2 million in 2019, 2018 and 2017, respectively, to the 401(k) Plan. Deferred Compensation Plan The Company provides a nonqualified deferred compensation plan which is intended to be an unfunded plan. The plan's primary purpose is to provide a tax-deferred capital accumulation vehicle for a select group of management, highly compensated employees and non-employee members of the Board of Directors of the Company and to supplement such employees' 401(k) Plan contributions as well as offering this plan to be competitive in the marketplace. Eligible employees who enroll in the plan have the following deferral options: (i) eligible employees may elect to defer up to a maximum of 70 percent of base salary and 100 percent of annual bonus awards or (ii) eligible employees may elect a deferral percentage of base salary and bonus awards based on the deferral percentage elected for a year under the 401(k) Plan with such deferrals to start when maximum deferrals to the qualified 401(k) Plan have been made because of limitations in that plan. Eligible directors who enroll in the plan may elect to defer up to a maximum of 100 percent of directors' meeting fees and annual retainers. The Company matches employee (but not non-employee director) deferrals to make up for any match lost in the 401(k) Plan because of deferrals to the deferred compensation plan and to allow for a match that would have been made under the 401(k) Plan on that portion of either the first six percent of total compensation or the first five percent of total compensation, depending on prior participant elections, deferred that exceeds the limits allowed in the 401(k) Plan. Matching credits vest based on years of service, with full vesting after three years or, if earlier, on retirement, disability, death, a change in control of the Company or termination of the plan. Deferrals, plus any Company match, are credited to a recordkeeping account in the participant's name. Earnings on the deferrals are indexed to the assumed investment funds selected by the participant. In 2019, those investment options included a Company Common Stock fund, whose value was determined based on the stock price of the Company's common stock. The Company accounts for the contributions related to the Company's executive officers in this plan as Accrued Benefit Obligations, and the Company accounts for the contributions related to the Company's directors in this plan as Other Deferred Credits and Other Liabilities in the Consolidated Balance Sheets. The investment associated with these contributions is accounted for as Other Property and Investments in the Consolidated Balance Sheets. The appreciation of these investments is accounted for as Other Income, and the increase in the liability under the plan is accounted for as Other Expense in the Consolidated Statements of Income.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Regulatory Assets and Liabilities [Table Text Block]	The following table is a summary of OG&E's regulatory assets and liabilities. December 31 (In millions) 2019 2018 REGULATORY ASSETS Current: Fuel clause under recoveries $ 39.5 $ 2.0 Production tax credit rider over credit (A) 1.7 6.9 Oklahoma demand program rider under recovery (A) — 6.4 Other (A) 7.5 3.2 Total current regulatory assets $ 48.7 $ 18.5 Non-current: Benefit obligations regulatory asset $ 167.2 $ 188.2 Deferred storm expenses 65.5 36.5 Sooner Dry Scrubbers 20.6 4.5 Smart Grid 18.4 25.6 Unamortized loss on reacquired debt 10.6 11.4 Arkansas deferred pension expenses 8.0 6.8 Pension tracker 2.3 — Other 13.4 12.8 Total non-current regulatory assets $ 306.0 $ 285.8 REGULATORY LIABILITIES Current: Reserve for tax refund and interim surcharge (B) $ 12.7 $ 15.4 Fuel clause over recoveries 4.8 0.3 SPP cost tracker over recovery (B) 2.6 16.8 Oklahoma demand program rider over recovery (B) 2.0 — Transmission cost recovery rider over recovery (B) — 2.7 Other (B) 6.9 1.4 Total current regulatory liabilities $ 29.0 $ 36.6 Non-current: Income taxes refundable to customers, net $ 899.2 $ 937.1 Accrued removal obligations, net 318.5 308.1 Pension tracker — 18.7 Other 5.8 6.8 Total non-current regulatory liabilities $ 1,223.5 $ 1,270.7 (A) Included in Other Current Assets in the Consolidated Balance Sheets.
Components of Benefit Obligation Regulatory Asset [Table Text Block]	The following table is a summary of the components of the benefit obligations regulatory asset: December 31 (In millions) 2019 2018 Pension Plan and Restoration of Retirement Income Plan: Net loss $ 160.5 $ 185.3 Postretirement Benefit Plans: Net loss 23.3 25.6 Prior service cost (16.6) (22.7) Total $ 167.2 $ 188.2
Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block]	The following amounts in the benefit obligations regulatory asset at December 31, 2019 are expected to be recognized as components of net periodic benefit cost in 2020: (In millions) Pension Plan and Restoration of Retirement Income Plan: Net loss $ 11.4 Postretirement Benefit Plans: Net loss 2.8 Prior service cost (6.1) Total $ 8.1
Schedule of Jointly Owned Utility Plants [Table Text Block]	The tables below present OG&E's ownership interest in the jointly-owned McClain Plant and the jointly-owned Redbud Plant, and, as disclosed below, only OG&E's ownership interest is reflected in the property, plant and equipment and accumulated depreciation balances in these tables. The owners of the remaining interests in the McClain Plant and the Redbud Plant are responsible for providing their own financing of capital expenditures. Also, only OG&E's proportionate interests of any direct expenses of the McClain Plant and the Redbud Plant, such as fuel, maintenance expense and other operating expenses, are included in the applicable financial statement captions in the Consolidated Statements of Income. December 31, 2019 (In millions) Percentage Ownership Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment McClain Plant (A) 77 % $ 254.4 $ 83.5 $ 170.9 Redbud Plant (A)(B) 51 % $ 529.9 $ 159.0 $ 370.9 (A) Construction work in progress was $0.2 million and $1.4 million for the McClain and Redbud Plants, respectively. (B) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million. December 31, 2018 (In millions) Percentage Ownership Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment McClain Plant (A) 77 % $ 227.2 $ 78.2 $ 149.0 Redbud Plant (A)(B) 51 % $ 493.9 $ 145.3 $ 348.6 (A) Construction work in progress was $0.2 million and $0.9 million for the McClain and Redbud Plants, respectively. (B) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million.
Property, Plant and Equipment [Table Text Block]	The Company's property, plant and equipment and related accumulated depreciation are divided into the following major classes: December 31, 2019 (In millions) Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment OGE Energy: Property, plant and equipment $ 6.1 $ — $ 6.1 OGE Energy property, plant and equipment 6.1 — 6.1 OG&E: Distribution assets 4,468.6 1,381.1 3,087.5 Electric generation assets (A) 4,838.6 1,601.0 3,237.6 Transmission assets (B) 2,901.1 565.5 2,335.6 Intangible plant 225.2 145.4 79.8 Other property and equipment 473.1 175.1 298.0 OG&E property, plant and equipment 12,906.6 3,868.1 9,038.5 Total property, plant and equipment $ 12,912.7 $ 3,868.1 $ 9,044.6 (A) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million. (B) This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.8 million. December 31, 2018 (In millions) Total Property, Plant and Equipment Accumulated Depreciation Net Property, Plant and Equipment OGE Energy: Property, plant and equipment $ 6.1 $ — $ 6.1 OGE Energy property, plant and equipment 6.1 — 6.1 OG&E: Distribution assets 4,229.4 1,324.5 2,904.9 Electric generation assets (A) 4,657.2 1,572.8 3,084.4 Transmission assets (B) 2,846.7 534.2 2,312.5 Intangible plant 187.6 135.1 52.5 Other property and equipment 444.2 160.8 283.4 OG&E property, plant and equipment 12,365.1 3,727.4 8,637.7 Total property, plant and equipment $ 12,371.2 $ 3,727.4 $ 8,643.8 (A) This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million. (B) This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.7 million.
Schedule of Computer Software Costs, Amortization [Table Text Block]	The following table summarizes the Company's amortization expense for computer software costs. Year Ended December 31 (In millions) 2019 2018 2017 OGE Energy $ — $ — $ 0.2 OG&E 11.0 9.6 8.8 Total $ 11.0 $ 9.6 $ 9.0
Schedule of Change in Asset Retirement Obligation [Table Text Block]	The following table summarizes changes to the Company's asset retirement obligations during the years ended December 31, 2019 and 2018. (In millions) 2019 2018 Balance at January 1 $ 83.9 $ 75.1 Accretion expense 1.0 3.4 Revisions in estimated cash flows (A) (2.4) 6.8 Liabilities settled (B) (9.0) (1.4) Balance at December 31 $ 73.5 $ 83.9 (A) Assumptions changed related to the estimated cost of the removal of wind turbine assets and asbestos removal at OG&E's generating facilities.
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following tables summarize changes in the components of accumulated other comprehensive income (loss) attributable to the Company during 2018 and 2019. All amounts below are presented net of tax. Pension Plan and Restoration of Retirement Income Plan Postretirement Benefit Plans (In millions) Net Gain Net Gain (Loss) Prior Service Cost (Credit) Other Comprehensive Loss from Unconsolidated Affiliates Total Balance at December 31, 2017 $ (32.7) $ 2.5 $ 7.0 $ — $ (23.2) Other comprehensive income (loss) before reclassifications (14.1) 2.1 — — (12.0) Amounts reclassified from accumulated other comprehensive income (loss) 3.3 — (1.7) — 1.6 Settlement cost 4.7 — — — 4.7 Net current period other comprehensive income (loss) (6.1) 2.1 (1.7) — (5.7) Balance at December 31, 2018 (38.8) 4.6 5.3 — (28.9) Other comprehensive income (loss) before reclassifications (8.3) (0.2) — (0.6) (9.1) Amounts reclassified from accumulated other comprehensive income (loss) 3.4 (0.2) (1.7) — 1.5 Settlement cost 8.6 — — — 8.6 Net current period other comprehensive income (loss) 3.7 (0.4) (1.7) (0.6) 1.0 Balance at December 31, 2019 $ (35.1) $ 4.2 $ 3.6 $ (0.6) $ (27.9)
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	The following table summarizes significant amounts reclassified out of accumulated other comprehensive income (loss) by the respective line items in net income during the years ended December 31, 2019 and 2018. Details about Accumulated Other Comprehensive Income (Loss) Components Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Consolidated Statements of Income Year Ended December 31, (In millions) 2019 2018 Amortization of Pension Plan and Restoration of Retirement Income Plan items: Actuarial losses $ (4.5) $ (4.4) (A) Settlement cost (11.3) (6.3) (A) (15.8) (10.7) Income Before Taxes (3.8) (2.7) Income Tax Expense $ (12.0) $ (8.0) Net Income Amortization of postretirement benefit plans items: Prior service credit $ 2.3 $ 2.3 (A) Actuarial gains 0.2 — (A) 2.5 2.3 Income Before Taxes 0.6 0.6 Income Tax Expense $ 1.9 $ 1.7 Net Income Total reclassifications for the period, net of tax $ (10.1) $ (6.3) Net Income (A) These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost (see Note 13 for additional information).
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block]	The amounts in accumulated other comprehensive loss (gain) at December 31, 2019 that are expected to be recognized into earnings in 2020 are as follows: (In millions) Pension Plan and Restoration of Retirement Income Plan: Net gain $ (4.2) Postretirement Benefit Plans: Net loss 0.2 Prior service cost 2.3 Total, net of tax $ (1.7)

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	The following table disaggregates the Company's revenues from contracts with customers by customer classification. The Company's operating revenues disaggregated by customer classification can be found in "OG&E (Electric Utility) Results of Operations" within "Item 7. Management's Discussion and Analysis of Financial Condition and Results of Operations." Year Ended December 31, (In millions) 2019 2018 Residential $ 865.8 $ 877.8 Commercial 486.6 500.0 Industrial 217.8 228.9 Oilfield 200.4 190.4 Public authorities and street light 190.3 197.4 System sales revenues 1,960.9 1,994.5 Provision for rate refund (0.9) (6.0) Integrated market 38.4 48.7 Transmission 148.0 147.4 Other 29.1 27.1 Revenues from contracts with customers $ 2,175.5 $ 2,211.7

Leases, Codification Topic 842

Leases, Codification Topic 842 (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Lease, Cost	The following table presents amounts recognized for operating leases in the Company's 2019 Consolidated Cash Flow Statement and Balance Sheet and supplemental information related to those amounts recognized, as well as a maturity analysis of the Company's operating lease liabilities. (In millions) Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 5.6 Right-of-use assets obtained in exchange for new operating lease liabilities $ 10.7 (Dollars in millions) December 31, 2019 Right-of-use assets at period end (A) $ 40.9 Operating lease liabilities at period end (B) $ 45.8 Operating lease weighted-average remaining lease term (in years) 13.1 Operating lease weighted-average discount rate 3.9 % December 31, Future minimum operating lease payments as of: 2019 2018(C)(D) (In millions) 2019 $ — $ 22.1 2020 6.2 3.9 2021 5.8 3.5 2022 5.2 2.9 2023 5.2 2.9 2024 3.1 3.0 Thereafter 34.7 34.6 Total future minimum lease payments 60.2 $ 72.9 Less: Imputed interest 14.4 Present value of net minimum lease payments $ 45.8 (A) Included in Property, Plant and Equipment in the 2019 Consolidated Balance Sheet. (B) Included in Other Deferred Credits and Other Liabilities in the 2019 Consolidated Balance Sheet. (C) Amounts included for comparability and accounted for in accordance with ASC 840, "Leases." (D) At the end of the railcar lease term, which was February 1, 2019, OG&E had the option to either purchase the railcars at a stipulated fair market value or renew the lease. OG&E renewed the lease effective February 1, 2019. If OG&E chose not to purchase the railcars or renew the lease agreement and the actual fair value of the railcars was less than the stipulated fair market value, OG&E would have been responsible for the difference in those values up to a maximum of $16.2 million.

Investment in Unconsolidated _2

Investment in Unconsolidated Affiliate and Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Summarized Balance Sheet Financial Information, Equity Method Investment [Table Text Block]	Summarized unaudited financial information for 100 percent of Enable is presented below as of December 31, 2019 and 2018 and for the years ended December 31, 2019, 2018 and 2017. December 31, Balance Sheet 2019 2018 (In millions) Current assets $ 389 $ 449 Non-current assets $ 11,877 $ 11,995 Current liabilities $ 780 $ 1,615 Non-current liabilities $ 4,077 $ 3,211
Summarized Income Statement Financial Information, Equity Method Investment [Table Text Block]	Year Ended December 31, Income Statement 2019 2018 2017 (In millions) Total revenues $ 2,960 $ 3,431 $ 2,803 Cost of natural gas and NGLs $ 1,279 $ 1,819 $ 1,381 Operating income $ 569 $ 648 $ 528 Net income $ 360 $ 485 $ 400
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Table Text Block]	The following table reconciles OGE Energy's equity in earnings of unconsolidated affiliates for the years ended December 31, 2019, 2018 and 2017. Year Ended December 31, (In millions) 2019 2018 2017 Enable net income $ 360.0 $ 485.3 $ 400.3 OGE Energy's percent ownership at period end 25.5 % 25.6 % 25.7 % OGE Energy's portion of Enable net income $ 91.8 $ 124.4 $ 102.7 Amortization of basis difference and dilution recognition (A) 22.1 28.4 28.5 Equity in earnings of unconsolidated affiliates $ 113.9 $ 152.8 $ 131.2 (A) Includes loss on dilution, net of proportional basis difference recognition.
Reconciliation of Basis Difference [Table Text Block]	The following table reconciles the difference between OGE Energy's investment in Enable and its underlying equity in the net assets of Enable (basis difference) from December 31, 2018 to December 31, 2019. (In millions) Basis difference at December 31, 2018 $ 680.3 Amortization of basis difference (A) (27.8) Basis difference at December 31, 2019 $ 652.5 (A) Includes proportional basis difference recognition due to dilution.
Schedule of Related Party Transactions [Table Text Block]	The following table summarizes related party transactions between OG&E and Enable during the years ended December 31, 2019, 2018 and 2017. Year Ended December 31, (In millions) 2019 2018 2017 Operating revenues: Electricity to power electric compression assets $ 15.9 $ 16.3 $ 14.0 Cost of sales: Natural gas transportation services $ 41.2 $ 37.9 $ 35.0 Natural gas (sales) purchases $ (6.0) $ (3.2) $ (2.1)

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping [Table Text Block]	The following table summarizes the carrying amount and fair value of the Company's financial instruments at December 31, 2019 and 2018, as well as the classification level within the fair value hierarchy. 2019 2018 December 31 (In millions) Carrying Amount Fair Carrying Amount Fair Classification Long-term Debt (including Long-term Debt due within one year): OG&E Senior Notes $ 3,050.3 $ 3,500.4 $ 3,001.9 $ 3,178.2 Level 2 OG&E Industrial Authority Bonds $ 135.4 $ 135.4 $ 135.4 $ 135.4 Level 2 Tinker Debt $ 9.5 $ 10.0 $ 9.6 $ 8.7 Level 3

Stock Based Compensation (Table

Stock Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Stock-Based Compensation [Abstract]
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	The following table summarizes the Company's pre-tax compensation expense and related income tax benefit for the years ended December 31, 2019, 2018 and 2017 related to the Company's performance units and restricted stock units. Year Ended December 31 (In millions) 2019 2018 2017 Performance units: Total shareholder return $ 8.7 $ 8.2 $ 7.6 Earnings per share 4.3 5.1 1.4 Total performance units 13.0 13.3 9.0 Restricted stock units 0.9 0.1 0.1 Total compensation expense $ 13.9 $ 13.4 $ 9.1 Income tax benefit $ 3.6 $ 3.4 $ 3.5
Performance Units Total Shareholder Return Valuation Assumptions [Table Text Block]	The number of performance units granted based on total shareholder return and the assumptions used to calculate the grant date fair value of the performance units based on total shareholder return are shown in the following table. 2019 2018 2017 Number of units granted 208,647 261,916 260,570 Fair value of units granted $ 47.00 $ 36.86 $ 41.77 Expected dividend yield 4.0 % 3.6 % 3.8 % Expected price volatility 17.0 % 19.0 % 19.9 % Risk-free interest rate 2.47 % 2.38 % 1.44 % Expected life of units (in years) 2.86 2.86 2.80
Performance Units Earnings Per Share Valuation Assumptions [Table Text Block]	In 2019, the Compensation Committee of the Company's Board of Directors voted to grant restricted stock units in lieu of performance units based on earnings per share. For 2018 and 2017, the number of performance units granted based on earnings per share and the grant date fair value are shown in the following table. 2018 2017 Number of units granted 87,308 86,857 Fair value of units granted $ 31.03 $ 34.83
Restricted Stock Valuation Assumptions [Table Text Block]	The number of restricted stock units granted and the grant date fair value are shown in the following table. 2019 2018 2017 Restricted stock units granted 75,929 826 3,145 Fair value of restricted stock units granted $ 41.71 $ 36.28 $ 34.96
Share-based Compensation, Activity [Table Text Block]	A summary of the activity for the Company's performance units and restricted stock units at December 31, 2019 and changes in 2019 are shown in the following table. Performance Units Restricted Total Shareholder Return Earnings Per Share (Dollars in millions) Number Aggregate Intrinsic Value Number Aggregate Intrinsic Value Number Aggregate Intrinsic Value Units/shares outstanding at 12/31/18 755,480 251,825 2,711 Granted 208,647 (A) — 75,929 Converted (274,078) (B) $ 19.8 (91,356) (B) $ 7.2 N/A Vested N/A N/A (2,161) $ 0.1 Forfeited (25,232) (5,298) (3,599) Units/shares outstanding at 12/31/19 664,817 $ 35.4 155,171 $ 11.5 72,880 $ 3.2 Units/shares fully vested at 12/31/19 222,163 $ 11.5 74,053 $ 6.6 (A) For performance units, this represents the target number of performance units granted. Actual number of performance units earned, if any, is dependent upon performance and may range from zero percent to 200 percent of the target.
Schedule of Nonvested Share Activity [Table Text Block]	A summary of the activity for the Company's non-vested performance units and restricted stock units at December 31, 2019 and changes in 2019 are shown in the following table. Performance Units Restricted Total Shareholder Return Earnings Per Share Number Weighted-Average Number Weighted-Average Number Weighted-Average Units/shares non-vested at 12/31/18 481,402 $ 39.17 160,469 $ 32.82 2,711 $ 35.00 Granted 208,647 (A) $ 47.00 — $ — 75,929 $ 41.71 Vested (222,163) $ 41.76 (74,053) $ 34.83 (2,161) $ 34.66 Forfeited (25,232) $ 41.45 (5,298) $ 32.07 (3,599) $ 41.78 Units/shares non-vested at 12/31/19 442,654 $ 41.43 81,118 $ 31.03 72,880 $ 41.66 Units/shares expected to vest 418,331 (B) 77,617 (B) 54,102 (B) (A) For performance units, this represents the target number of performance units granted. Actual number of performance units earned, if any, is dependent upon performance and may range from zero percent to 200 percent of the target. (B) The intrinsic value of the performance units based on total shareholder return and earnings per share is $22.8 million and $4.7 million, respectively. The intrinsic value of restricted stock units is $2.4 million.
Fair Value of Vested Performance Units and Restricted Stock [Table Text Block]	A summary of the Company's fair value for its vested performance units and restricted stock units is shown in the following table. Year Ended December 31 (In millions) 2019 2018 2017 Performance units: Total shareholder return $ 9.3 $ 5.9 $ 6.3 Earnings per share $ 5.2 $ 4.9 $ 1.2 Restricted stock units $ 0.1 $ 0.1 $ 0.1
Schedule of Unrecognized Compensation Cost, Nonvested Awards [Table Text Block]	A summary of the Company's unrecognized compensation cost for its non-vested performance units and restricted stock units and the weighted-average periods over which the compensation cost is expected to be recognized are shown in the following table. December 31, 2019 Unrecognized Compensation Cost (In millions) Weighted Average to be Recognized (In years) Performance units: Total shareholder return $ 8.7 1.67 Earnings per share 0.8 1.00 Total performance units 9.5 Restricted stock units 1.5 1.98 Total unrecognized compensation cost $ 11.0

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	The following table presents information about investing and financing activities that affected recognized assets and liabilities but did not result in cash receipts or payments. Cash paid for interest, net of interest capitalized, and cash paid for income taxes, net of income tax refunds are also presented in the table. Year Ended December 31 (In millions) 2019 2018 2017 NON-CASH INVESTING AND FINANCING ACTIVITIES Power plant long-term service agreement $ 28.9 $ (9.2) $ (2.6) SUPPLEMENTAL CASH FLOW INFORMATION Cash paid during the period for: Interest (net of interest capitalized) (A) $ 152.2 $ 153.8 $ 139.6 Income taxes (net of income tax refunds) $ 5.5 $ 2.8 $ (16.0)

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Taxes [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The items comprising income tax expense (benefit) are as follows: Year Ended December 31 (In millions) 2019 2018 2017 Provision (benefit) for current income taxes: Federal $ (6.4) $ (1.9) $ 4.9 State 5.1 (4.4) (4.2) Total provision (benefit) for current income taxes (1.3) (6.3) 0.7 Provision (benefit) for deferred income taxes, net: Federal 48.5 74.7 (75.9) State (17.4) 3.7 26.0 Total provision (benefit) for deferred income taxes, net 31.1 78.4 (49.9) Deferred federal investment tax credits, net — 0.1 (0.1) Total income tax expense (benefit) $ 29.8 $ 72.2 $ (49.3)
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following schedule reconciles the statutory tax rates to the effective income tax rate: Year Ended December 31 2019 2018 2017 Statutory federal tax rate 21.0 % 21.0 % 35.0 % Executive compensation limitation 0.2 0.2 — Federal renewable energy credit (A) (6.0) (5.1) (4.8) Amortization of net unfunded deferred taxes (4.5) (2.1) 0.7 State income taxes, net of federal income tax benefit (1.2) 0.4 2.0 Stock-based compensation (1.2) — — Remeasurement of state deferred tax liabilities (0.8) (0.4) 0.4 Other (0.7) 0.4 (0.1) 401(k) dividends (0.4) (0.3) (0.5) Federal deferred tax revaluation — 0.4 (41.2) Federal investment tax credits, net — — (0.1) Effective income tax rate 6.4 % 14.5 % (8.6) %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The components of Deferred Income Taxes at December 31, 2019 and 2018 were as follows: December 31 (In millions) 2019 2018 Deferred income tax liabilities, net: Accelerated depreciation and other property related differences $ 1,656.8 $ 1,605.3 Investment in Enable 478.2 469.9 Regulatory assets 28.4 17.4 Company Pension Plan 4.1 7.6 Bond redemption-unamortized costs 2.2 2.4 Derivative instruments 1.6 1.7 Other 0.4 1.1 Federal tax credits (238.0) (237.8) Income taxes recoverable from customers, net (229.9) (239.6) State tax credits (185.8) (156.0) Regulatory liabilities (68.1) (78.8) Postretirement medical and life insurance benefits (23.3) (23.6) Asset retirement obligations (19.2) (21.5) Net operating losses (16.6) (20.2) Accrued liabilities (10.7) (12.5) Accrued vacation (2.1) (2.3) Deferred federal investment tax credits (1.8) (1.8) Uncollectible accounts (0.4) (0.4) Total deferred income tax liabilities, net $ 1,375.8 $ 1,310.9
Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]	Following is a reconciliation of the Company's total gross unrecognized tax benefits as of the years ended December 31, 2019, 2018 and 2017. (In millions) 2019 2018 2017 Balance at January 1 $ 20.7 $ 20.7 $ 20.7 Tax positions related to current year: Additions — — — Balance at December 31 $ 20.7 $ 20.7 $ 20.7
Summary of Tax Credit Carryforwards [Table Text Block]	The following table summarizes these carry forwards: (In millions) Carry Forward Amount Deferred Tax Asset Earliest Expiration Date State operating loss $ 371.6 $ 16.6 2030 Federal tax credits $ 238.0 $ 238.0 2032 State tax credits: Oklahoma investment tax credits $ 183.9 $ 145.3 N/A Oklahoma capital investment board credits $ 12.4 $ 12.4 N/A Oklahoma zero emission tax credits $ 34.9 $ 28.0 2020 Louisiana inventory credits $ 0.2 $ 0.1 2020 N/A - not applicable

Common Equity (Tables)

Common Equity (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table calculates basic and diluted earnings per share for the Company. (In millions except per share data) 2019 2018 2017 Net income $ 433.6 $ 425.5 $ 619.0 Average common shares outstanding: Basic average common shares outstanding 200.1 199.7 199.7 Effect of dilutive securities: Contingently issuable shares (performance and restricted stock units) 0.6 0.8 0.3 Diluted average common shares outstanding 200.7 200.5 200.0 Basic earnings per average common share $ 2.17 $ 2.13 $ 3.10 Diluted earnings per average common share $ 2.16 $ 2.12 $ 3.10 Anti-dilutive shares excluded from earnings per share calculation — — —

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2019
Long-term Debt, Unclassified [Abstract]
Schedule of Long-term Debt Instruments [Table Text Block]	OG&E has tax-exempt pollution control bonds with optional redemption provisions that allow the holders to request repayment of the bonds on any business day. The bonds, which can be tendered at the option of the holder during the next 12 months, are as follows: Series Date Due Amount (In millions) 1.20% - 2.50% Garfield Industrial Authority, January 1, 2025 $ 47.0 1.19% - 2.35% Muskogee Industrial Authority, January 1, 2025 32.4 1.20% - 2.48% Muskogee Industrial Authority, June 1, 2027 56.0 Total (redeemable during next 12 months) $ 135.4

Short-Term Debt and Credit Fa_2

Short-Term Debt and Credit Facilities (Tables)	12 Months Ended
	Dec. 31, 2019
Short-term Debt [Abstract]
Schedule of Line of Credit Facilities [Table Text Block]	The following table provides information regarding the Company's revolving credit agreements at December 31, 2019. Aggregate Amount Weighted-Average Entity Commitment Outstanding (A) Interest Rate Expiration (In millions) OGE Energy (B) $ 450.0 $ 112.0 2.06 % (D) March 8, 2023 OG&E (C) 450.0 0.3 1.00 % (D) March 8, 2023 Total $ 900.0 $ 112.3 2.06 % (A) Includes direct borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit at December 31, 2019. (B) This bank facility is available to back up the Company's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility. (C) This bank facility is available to back up OG&E's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility. (D) Represents the weighted-average interest rate for the outstanding borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit.

Retirement Plans and Postreti_2

Retirement Plans and Postretirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Retirement Plans and Postretirement Benefit Plans [Abstract]
Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets [Table Text Block]	The following table presents the status of the Company's Pension Plan, the Restoration of Retirement Income Plan and the postretirement benefit plans for 2019 and 2018. These amounts have been recorded in Accrued Benefit Obligations with the offset in Accumulated Other Comprehensive Loss (except OG&E's portion, which is recorded as a regulatory asset as discussed in Note 1) in the Company's Consolidated Balance Sheets. The amounts in Accumulated Other Comprehensive Loss and those recorded as a regulatory asset represent a net periodic benefit cost to be recognized in the Consolidated Statements of Income in future periods. The benefit obligation for the Company's Pension Plan and the Restoration of Retirement Income Plan represents the projected benefit obligation, while the benefit obligation for the postretirement benefit plans represents the accumulated postretirement benefit obligation. The accumulated postretirement benefit obligation for the Company's Pension Plan and Restoration of Retirement Income Plan differs from the projected benefit obligation in that the former includes no assumption about future compensation levels. The accumulated postretirement benefit obligation for the Pension Plan and the Restoration of Retirement Income Plan at December 31, 2019 was $563.3 million and $8.1 million, respectively. The accumulated postretirement benefit obligation for the Pension Plan and the Restoration of Retirement Income Plan at December 31, 2018 was $561.9 million and $7.8 million, respectively. The details of the funded status of the Pension Plan, the Restoration of Retirement Income Plan and the postretirement benefit plans and the amounts included in the Consolidated Balance Sheets are included in the following table. Pension Plan Restoration of Retirement Postretirement December 31 (In millions) 2019 2018 2019 2018 2019 2018 Change in benefit obligation Beginning obligations $ 615.9 $ 687.5 $ 9.6 $ 8.1 $ 135.8 $ 149.4 Service cost 12.9 14.9 0.5 0.4 0.2 0.3 Interest cost 20.7 23.8 0.4 0.3 5.6 5.4 Plan settlements (83.1) (73.7) (1.2) (2.0) — — Plan amendments — — 0.3 — — — Participants' contributions — — — — 4.1 3.8 Actuarial losses (gains) 64.3 (22.0) 0.7 2.8 2.9 (9.6) Benefits paid (14.6) (14.6) — — (12.1) (13.5) Ending obligations $ 616.1 $ 615.9 $ 10.3 $ 9.6 $ 136.5 $ 135.8 Change in plans' assets Beginning fair value $ 522.8 $ 635.3 $ — $ — $ 45.3 $ 50.2 Actual return on plans' assets 85.2 (39.2) — — 4.6 (0.6) Employer contributions 20.0 15.0 1.2 2.0 5.1 5.4 Plan settlements (83.1) (73.7) (1.2) (2.0) — — Participants' contributions — — — — 4.1 3.8 Benefits paid (14.6) (14.6) — — (12.1) (13.5) Ending fair value $ 530.3 $ 522.8 $ — $ — $ 47.0 $ 45.3 Funded status at end of year $ (85.8) $ (93.1) $ (10.3) $ (9.6) $ (89.5) $ (90.5)
Schedule of Defined Benefit Plans Disclosures [Table Text Block]	The following table presents the net periodic benefit cost components, before consideration of capitalized amounts, of the Company's Pension Plan, Restoration of Retirement Income Plan and postretirement benefit plans that are included in the Consolidated Financial Statements. Service cost is presented within Other Operation and Maintenance, and interest cost, expected return on plan assets, amortization of net loss, amortization of unrecognized prior service cost and settlement cost are presented within Other Net Periodic Benefit Expense in the Company's Consolidated Statements of Income. OG&E recovers specific amounts of pension and postretirement medical costs in rates approved in its Oklahoma rate reviews. In accordance with approved orders, OG&E defers the difference between actual pension and postretirement medical expenses and the amount approved in its last Oklahoma rate review as a regulatory asset or regulatory liability. These amounts have been recorded in the Pension tracker in the regulatory assets and liabilities table in Note 1 and within Other Net Periodic Benefit Expense in the Company's Consolidated Statements of Income. Pension Plan Restoration of Retirement Postretirement Benefit Plans Year Ended December 31 (In millions) 2019 2018 2017 2019 2018 2017 2019 2018 2017 Service cost $ 12.9 $ 14.9 $ 15.5 $ 0.5 $ 0.4 $ 0.3 $ 0.2 $ 0.3 $ 0.6 Interest cost 20.7 23.8 26.2 0.4 0.3 0.3 5.6 5.4 7.2 Expected return on plan assets (36.1) (44.1) (42.6) — — — (1.9) (2.0) (2.2) Amortization of net loss 17.3 16.2 17.4 0.5 0.7 0.4 2.0 3.8 2.0 Amortization of unrecognized prior service cost (A) — — (0.1) — 0.1 0.1 (8.4) (8.4) (3.5) Settlement cost 27.6 25.1 15.3 0.5 1.0 — — — 0.6 Total net periodic benefit cost 42.4 35.9 31.7 1.9 2.5 1.1 (2.5) (0.9) 4.7 Less: Amount paid by unconsolidated affiliates 2.9 2.5 4.3 0.1 0.1 — (0.6) (0.5) 0.3 Net periodic benefit cost $ 39.5 $ 33.4 $ 27.4 $ 1.8 $ 2.4 $ 1.1 $ (1.9) $ (0.4) $ 4.4 (A) Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment. In addition to the net periodic benefit cost amounts recognized, as presented in the table above, for the Pension and Restoration of Retirement Income Plans in 2019, 2018 and 2017, the Company recognized the following: Year Ended December 31 (In millions) 2019 2018 2017 Decrease of pension expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) $ (16.1) $ (14.1) $ (2.3) Deferral of pension expense related to pension settlement charges: Oklahoma jurisdiction (A) $ 17.9 $ 22.1 $ 13.2 Arkansas jurisdiction (A) $ 1.7 $ 2.1 $ 1.1 (A) Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1. In addition to the net periodic benefit income and cost amounts recognized, as presented in the table above, for the postretirement benefit plans in 2019, 2018 and 2017, the Company recognized the following: Year Ended December 31 (In millions) 2019 2018 2017 Increase of postretirement expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) $ 1.0 $ 4.4 $ 6.2
Schedule of Capitalized Pension and Postretirement Cost [Table Text Block]	(In millions) 2019 2018 2017 Capitalized portion of net periodic pension benefit cost $ 3.6 $ 3.8 $ 4.4 Capitalized portion of net periodic postretirement benefit cost $ 0.2 $ 0.2 $ 1.2
Schedule of Assumptions Used [Table Text Block]	Rate Assumptions Pension Plan and Postretirement Year Ended December 31 2019 2018 2017 2019 2018 2017 Assumptions to determine benefit obligations: Discount rate 3.15 % 4.20 % 3.60 % 3.25 % 4.30 % 3.70 % Rate of compensation increase 4.20 % 4.20 % 4.20 % N/A N/A N/A Assumptions to determine net periodic benefit cost: Discount rate 3.63 % 3.73 % 4.00 % 4.30 % 3.70 % 4.20 % Expected return on plan assets 7.50 % 7.50 % 7.50 % 4.00 % 4.00 % 4.00 % Rate of compensation increase 4.20 % 4.20 % 4.20 % N/A N/A 4.20 %
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]	The effects of a one-percentage point change in the assumed health care cost trend rate are presented in the following tables. ONE-PERCENTAGE POINT INCREASE Year Ended December 31 (In millions) 2019 2018 2017 Effect on aggregate of the service and interest cost components $ — $ — $ — Effect on accumulated postretirement benefit obligations $ 0.1 $ 0.1 $ 0.1 ONE-PERCENTAGE POINT DECREASE Year Ended December 31 (In millions) 2019 2018 2017 Effect on aggregate of the service and interest cost components $ — $ — $ — Effect on accumulated postretirement benefit obligations $ 0.3 $ 0.3 $ 0.3
Projected Benefit Obligation Funded Status Thresholds [Table Text Block]	The Pension Plan assets are held in a trust which follows an investment policy and strategy designed to reduce the funded status volatility of the Plan by utilizing liability driven investing. The purpose of liability-driven investing is to structure the asset portfolio to more closely resemble the pension liability and thereby more effectively hedge against changes in the liability. The investment policy follows a glide path approach that shifts a higher portfolio weighting to fixed income as the Plan's funded status increases. The table below sets forth the targeted fixed income and equity allocations at different funded status levels. Projected Benefit Obligation Funded Status Thresholds <90% 95% 100% 105% 110% 115% 120% Fixed income 50% 58% 65% 73% 80% 85% 90% Equity 50% 42% 35% 27% 20% 15% 10% Total 100% 100% 100% 100% 100% 100% 100%
Pension Plan Equity Asset Allocation Table [Table Text Block]	Within the portfolio's overall allocation to equities, the funds are allocated according to the guidelines in the table below. Asset Class Target Allocation Minimum Maximum Domestic Large Cap Equity 40% 35% 60% Domestic Mid-Cap Equity 15% 5% 25% Domestic Small-Cap Equity 25% 5% 30% International Equity 20% 10% 30%
Schedule of Allocation of Plan Assets [Table Text Block]	The following tables summarize the postretirement benefit plans' investments that are measured at fair value on a recurring basis at December 31, 2019 and 2018. There were no Level 2 investments held by the postretirement benefit plans at December 31, 2019 and 2018. (In millions) December 31, 2019 Level 1 Level 3 Group retiree medical insurance contract $ 34.8 $ — $ 34.8 Mutual funds 10.9 10.9 — Money market fund 1.2 1.2 — Total plan investments $ 46.9 $ 12.1 $ 34.8 (In millions) December 31, 2018 Level 1 Level 3 Group retiree medical insurance contract $ 36.0 $ — $ 36.0 Mutual funds 8.9 8.9 — Cash 0.9 0.9 — Total plan investments $ 45.8 $ 9.8 $ 36.0
Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]	The following table summarizes the postretirement benefit plans' investments that are measured at fair value on a recurring basis using significant unobservable inputs (Level 3). Year Ended December 31 (In millions) 2019 Group retiree medical insurance contract: Beginning balance $ 36.0 Claims paid (3.8) Investment fees (0.1) Net unrealized gains related to instruments held at the reporting date 1.4 Interest income 0.8 Dividend income 0.5 Ending balance $ 34.8
Schedule of Expected Benefit Payments [Table Text Block]	The following table summarizes the benefit payments the Company expects to pay related to OGE Energy's Pension Plan and Restoration of Retirement Income Plan. These expected benefits are based on the same assumptions used to measure the Company's benefit obligation at the end of the year and include benefits attributable to estimated future employee service. (In millions) Projected Benefit Payments 2020 $ 58.4 2021 $ 56.8 2022 $ 56.2 2023 $ 55.7 2024 $ 56.6 After 2024 $ 249.4 The Medicare Prescription Drug, Improvement and Modernization Act of 2003 expanded coverage for prescription drugs. The following table summarizes the gross benefit payments the Company expects to pay related to its postretirement benefit plans, including prescription drug benefits. (In millions) Gross Projected 2020 $ 11.2 2021 $ 11.2 2022 $ 11.1 2023 $ 9.5 2024 $ 9.4 After 2024 $ 42.3
Defined Benefit Plan, Plan Assets, Category	The following tables summarize the Pension Plan's investments that are measured at fair value on a recurring basis at December 31, 2019 and 2018. There were no Level 3 investments held by the Pension Plan at December 31, 2019 and 2018. (In millions) December 31, 2019 Level 1 Level 2 Net Asset Value (A) Common stocks $ 202.0 $ 202.0 $ — $ — U.S. Treasury notes and bonds (B) 134.8 134.8 — — Mortgage- and asset-backed securities 45.8 — 45.8 — Corporate fixed income and other securities 130.5 — 130.5 — Commingled fund (C) 23.9 — — 23.9 Foreign government bonds 3.0 — 3.0 — U.S. municipal bonds 1.1 — 1.1 — Money market fund 7.5 — — 7.5 Mutual fund 2.4 2.4 — — Preferred stocks 0.7 0.7 — — Futures: U.S. Treasury futures (receivable) 22.9 — 22.9 — U.S. Treasury futures (payable) (10.9) — (10.9) — Cash collateral 0.6 0.6 — — Forward contracts: Receivable (foreign currency) 0.1 — 0.1 — Total Pension Plan investments 564.4 $ 340.5 $ 192.5 $ 31.4 Interest and dividends receivable 2.4 Payable to broker for securities purchased (36.5) Total Pension Plan assets $ 530.3 (A) GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy. (B) This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher. (C) This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets. (In millions) December 31, 2018 Level 1 Level 2 Net Asset Value (A) Common stocks $ 169.3 $ 169.3 $ — $ — U.S. Treasury notes and bonds (B) 137.9 137.9 — — Mortgage- and asset-backed securities 65.9 — 65.9 — Corporate fixed income and other securities 143.2 — 143.2 — Commingled fund (C) 19.7 — — 19.7 Foreign government bonds 4.4 — 4.4 — U.S. municipal bonds 0.6 — 0.6 — Money market fund 0.3 — — 0.3 Mutual fund 8.0 8.0 — — Futures: U.S. Treasury futures (receivable) 27.0 — 27.0 — U.S. Treasury futures (payable) (20.4) — (20.4) — Cash collateral 0.7 0.7 — — Forward contracts: Receivable (foreign currency) 0.1 — 0.1 — Total Pension Plan investments 556.7 $ 315.9 $ 220.8 $ 20.0 Interest and dividends receivable 3.0 Payable to broker for securities purchased (36.9) Total Pension Plan assets $ 522.8 (A) GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy. (B) This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher.

Report of Business Segments (Ta

Report of Business Segments (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	The following tables summarize the results of the Company's business segments for the years ended December 31, 2019, 2018 and 2017. 2019 Electric Utility Natural Gas Midstream Operations Other Eliminations Total (In millions) Operating revenues $ 2,231.6 $ — $ — $ — $ 2,231.6 Cost of sales 786.9 — — — 786.9 Other operation and maintenance 492.5 2.8 (3.5) — 491.8 Depreciation and amortization 355.0 — — — 355.0 Taxes other than income 89.5 0.4 3.7 — 93.6 Operating income (loss) 507.7 (3.2) (0.2) — 504.3 Equity in earnings of unconsolidated affiliates — 113.9 — — 113.9 Other income (expense) 3.1 (8.6) 2.2 (3.6) (6.9) Interest expense 140.5 — 11.0 (3.6) 147.9 Income tax expense (benefit) 20.1 20.7 (11.0) — 29.8 Net income $ 350.2 $ 81.4 $ 2.0 $ — $ 433.6 Investment in unconsolidated affiliates $ — $ 1,132.9 $ 18.6 $ — $ 1,151.5 Total assets $ 10,076.6 $ 1,135.4 $ 107.0 $ (294.7) $ 11,024.3 Capital expenditures $ 635.5 $ — $ — $ — $ 635.5 2018 Electric Utility Natural Gas Midstream Operations Other Eliminations Total (In millions) Operating revenues $ 2,270.3 $ — $ — $ — $ 2,270.3 Cost of sales 892.5 — — — 892.5 Other operation and maintenance 473.8 1.4 (0.6) — 474.6 Depreciation and amortization 321.6 — — — 321.6 Taxes other than income 88.2 0.6 3.2 — 92.0 Operating income (loss) 494.2 (2.0) (2.6) — 489.6 Equity in earnings of unconsolidated affiliates — 152.8 — — 152.8 Other income (expense) 25.6 (4.9) (3.4) (6.0) 11.3 Interest expense 151.8 — 10.2 (6.0) 156.0 Income tax expense (benefit) 40.0 37.1 (4.9) — 72.2 Net income (loss) $ 328.0 $ 108.8 $ (11.3) $ — $ 425.5 Investment in unconsolidated affiliates $ — $ 1,166.6 $ 10.9 $ — $ 1,177.5 Total assets $ 9,704.5 $ 1,169.8 $ 184.8 $ (310.5) $ 10,748.6 Capital expenditures $ 573.6 $ — $ — $ — $ 573.6 2017 Electric Utility Natural Gas Midstream Operations Other Eliminations Total (In millions) Operating revenues $ 2,261.1 $ — $ — $ — $ 2,261.1 Cost of sales 897.6 — — — 897.6 Other operation and maintenance 469.8 (0.8) (10.3) — 458.7 Depreciation and amortization 280.9 — 2.6 — 283.5 Taxes other than income 84.8 1.0 3.6 — 89.4 Operating income (loss) 528.0 (0.2) 4.1 — 531.9 Equity in earnings of unconsolidated affiliates — 131.2 — — 131.2 Other income (expense) 57.7 (1.0) (5.4) (0.9) 50.4 Interest expense 138.4 — 6.3 (0.9) 143.8 Income tax expense (benefit) (A) 141.8 (195.2) 4.1 — (49.3) Net income (loss) $ 305.5 $ 325.2 $ (11.7) $ — $ 619.0 Investment in unconsolidated affiliates $ — $ 1,151.9 $ 8.5 $ — $ 1,160.4 Total assets $ 9,255.6 $ 1,155.3 $ 109.1 $ (107.3) $ 10,412.7 Capital expenditures $ 824.1 $ — $ — $ — $ 824.1

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Unrecorded Unconditional Purchase Obligations Disclosure [Table Text Block]	The Company's future purchase obligations and commitments estimated for the next five years are as follows: (In millions) 2020 2021 2022 2023 2024 Total Purchase obligations and commitments: Minimum purchase commitments $ 82.6 $ 55.1 $ 50.4 $ 50.4 $ 32.9 $ 271.4 Expected wind purchase commitments 55.7 56.0 56.4 56.8 57.5 282.4 Long-term service agreement commitments 2.4 2.4 2.4 13.8 32.1 53.1 Environmental compliance plan expenditures 0.4 — — — — 0.4 Total purchase obligations and commitments $ 141.1 $ 113.5 $ 109.2 $ 121.0 $ 122.5 $ 607.3
Schedule of Wind Power Purchases [Table Text Block]	The following table summarizes OG&E's wind power purchase contracts. Company Location Original Term of Contract Expiration of Contract MWs CPV Keenan Woodward County, OK 20 years 2030 152.0 Edison Mission Energy Dewey County, OK 20 years 2031 130.0 NextEra Energy Blackwell, OK 20 years 2032 60.0 The following table summarizes OG&E's wind power purchases for the years ended December 31, 2019, 2018 and 2017. Year Ended December 31 (In millions) 2019 2018 2017 CPV Keenan $ 27.2 $ 27.0 $ 29.0 Edison Mission Energy 23.1 21.7 22.1 NextEra Energy 7.4 6.8 7.4 FPL Energy (A) — 2.1 2.6 Total wind power purchased $ 57.7 $ 57.6 $ 61.1

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information [Table Text Block]	In the Company's opinion, the following quarterly financial data includes all adjustments, consisting of normal recurring adjustments, necessary to fairly present such amounts. Summarized consolidated quarterly unaudited financial data is as follows: Quarter Ended ( In millions, except per share data) March 31 June 30 September 30 December 31 Total Operating revenues 2019 $ 490.0 $ 513.7 $ 755.4 $ 472.5 $ 2,231.6 2018 $ 492.7 $ 567.0 $ 698.8 $ 511.8 $ 2,270.3 Operating income 2019 $ 49.7 $ 110.0 $ 274.3 $ 70.3 $ 504.3 2018 $ 66.6 $ 137.7 $ 227.3 $ 58.0 $ 489.6 Net income 2019 $ 47.1 $ 100.2 $ 250.9 $ 35.4 $ 433.6 2018 $ 55.0 $ 110.7 $ 205.1 $ 54.7 $ 425.5 Basic earnings per average common share (A) 2019 $ 0.24 $ 0.50 $ 1.25 $ 0.18 $ 2.17 2018 $ 0.28 $ 0.55 $ 1.03 $ 0.27 $ 2.13 Diluted earnings per average common share (A) 2019 $ 0.24 $ 0.50 $ 1.25 $ 0.18 $ 2.16 2018 $ 0.27 $ 0.55 $ 1.02 $ 0.27 $ 2.12

Schedule II (Tables)

Schedule II (Tables)	9 Months Ended
	Sep. 30, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II Valuation and Qualifying Accounts [Table Text Block]	SCHEDULE II - Valuation and Qualifying Accounts Additions Description Balance at Beginning of Period Charged to Costs and Expenses Deductions (A) Balance at End of Period (In millions) Balance at December 31, 2017 Reserve for Uncollectible Accounts $ 1.5 $ 2.6 $ 2.6 $ 1.5 Balance at December 31, 2018 Reserve for Uncollectible Accounts $ 1.5 $ 3.4 $ 3.2 $ 1.7 Balance at December 31, 2019 Reserve for Uncollectible Accounts $ 1.7 $ 2.2 $ 2.4 $ 1.5

Summary of Significant Accoun_4

Summary of Significant Accounting Policies Regulated Operations (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Fuel clause under recoveries		$ 39.5	$ 2
Fuel clause over recoveries		4.8	0.3
Regulatory Assets, Current		48.7	18.5
Regulatory Assets, Noncurrent		306	285.8
Regulatory Liability, Current		29	36.6
Regulatory Liability, Noncurrent		1,223.5	1,270.7
SPP Cost Tracker Rider Over Recovery [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	[1]	2.6	16.8
Reserve for Tax Refund [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	[1]	12.7	15.4
Transmission Cost Recovery Rider [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	[1]	0	2.7
Income taxes recoverable from customers, net [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Noncurrent		899.2	937.1
Accrued removal obligations [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Noncurrent		318.5	308.1
Pension tracker [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Noncurrent		0	18.7
Other Regulatory Liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	[1]	6.9	1.4
Regulatory Liability, Noncurrent		5.8	6.8
Oklahoma demand program rider over recovery
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	[1]	2	0
Production Tax Credit Rider [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	[2]	1.7	6.9
Oklahoma demand program rider under recovery [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	[2]	0	6.4
Benefit obligations regulatory asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		167.2	188.2
Deferred storm expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		65.5	36.5
Smart Grid [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		18.4	25.6
Unamortized loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		10.6	11.4
Deferred Pension Expenses [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		8	6.8
Dry Scrubber Regulatory Asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		20.6	4.5
Other Regulatory Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	[2]	7.5	3.2
Regulatory Assets, Noncurrent		13.4	12.8
Pension tracker [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Noncurrent		$ 2.3	$ 0
[1]	Included in Other Current Liabilities in the Consolidated Balance Sheets.
[2]	Included in Other Current Assets in the Consolidated Balance Sheets.

Summary of Significant Accoun_5

Summary of Significant Accounting Policies Accounting Records (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets, Current	$ 48.7	$ 18.5
Regulatory Assets, Noncurrent	306	285.8
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year	(1.7)
Deferred Storm and Property Reserve Deficiency, Current	2.7
Regulatory Liability, Current	29	36.6
Pension Plans, Defined Benefit [Member] | Defined Benefit Plans Income Loss [Member]
Components of Benefit Obligation Regulatory Asset	160.5	185.3
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year	11.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | Defined Benefit Plans Income Loss [Member]
Components of Benefit Obligation Regulatory Asset	23.3	25.6
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year	2.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | Prior Service Cost [Member]
Components of Benefit Obligation Regulatory Asset	(16.6)	$ (22.7)
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year	(6.1)
Regulatory Asset [Member]
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year	$ 8.1

Summary of Significant Accoun_6

Summary of Significant Accounting Policies Allowance for Uncollectible Accounts Receivable (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts Receivable	$ 1.5	$ 1.7

Summary of Significant Accoun_7

Summary of Significant Accounting Policies Fuel Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Other	$ 24.4	$ 29.5
Public Utilities, Inventory, Fuel [Member]
Public Utilities, Inventory	$ 46.3	$ 57.6

Summary of Significant Accoun_8

Summary of Significant Accounting Policies Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 12,912.7		$ 12,371.2
Accumulated Depreciation	3,868.1		3,727.4
Net property, plant and equipment	9,044.6		8,643.8
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	61.8		56.3
Capitalized Computer Software, Amortization	$ 11		$ 9.6		$ 9
McClain Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	77.00%	[1]	77.00%	[2]
Property, Plant and Equipment, Gross	$ 254.4	[1]	$ 227.2	[2]
Accumulated Depreciation	83.5	[1]	78.2	[2]
Net property, plant and equipment	170.9	[1]	149	[2]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	$ 0.2		$ 0.2
Redbud Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	51.00%	[1],[3]	51.00%	[2],[4]
Property, Plant and Equipment, Gross	$ 529.9	[1],[3]	$ 493.9	[2],[4]
Accumulated Depreciation	159	[1],[3]	145.3	[2],[4]
Net property, plant and equipment	370.9	[1],[3]	348.6	[2],[4]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	1.4		0.9
Amount of Acquisition Adjustments	148.3		148.3
OGE Energy [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	6.1		6.1
Accumulated Depreciation	0		0
Net property, plant and equipment	6.1		6.1
Capitalized Computer Software, Amortization	0		0		0.2
OGE Energy [Member] | Total Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	6.1		6.1
Accumulated Depreciation	0		0
Net property, plant and equipment	6.1		6.1
OG&E [Member]
Property, Plant and Equipment [Line Items]
Capitalized Computer Software, Gross	71.3		44.3
Capitalized Computer Software, Amortization	11		9.6		$ 8.8
OG&E [Member] | Total Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	12,906.6		12,365.1
Accumulated Depreciation	3,868.1		3,727.4
Net property, plant and equipment	9,038.5		8,637.7
OG&E [Member] | Electric Transmission and Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,468.6		4,229.4
Accumulated Depreciation	1,381.1		1,324.5
Net property, plant and equipment	3,087.5		2,904.9
OG&E [Member] | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,838.6	[5]	4,657.2	[6]
Accumulated Depreciation	1,601	[5]	1,572.8	[6]
Net property, plant and equipment	3,237.6	[5]	3,084.4	[6]
Amount of Acquisition Adjustments	148.3		148.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	61.8		56.3
OG&E [Member] | Electric Transmission [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,901.1	[7]	2,846.7	[8]
Accumulated Depreciation	565.5	[7]	534.2	[8]
Net property, plant and equipment	2,335.6	[7]	2,312.5	[8]
Amount of Acquisition Adjustments	3.3		3.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	0.8		0.7
OG&E [Member] | Finite-Lived Intangible Assets, Major Class Name [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	225.2		187.6
Accumulated Depreciation	145.4		135.1
Net property, plant and equipment	79.8		52.5
OG&E [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	473.1		444.2
Accumulated Depreciation	175.1		160.8
Net property, plant and equipment	$ 298		$ 283.4
[1]	Construction work in progress was $0.2 million and $1.4 million for the McClain and Redbud Plants, respectively.
[2]	Construction work in progress was $0.2 million and $0.9 million for the McClain and Redbud Plants, respectively.
[3]	This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million.
[4]	This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million.
[5]	This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million.
[6]	This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million.
[7]	This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.8 million.
[8]	This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.7 million.

Summary of Significant Accoun_9

Summary of Significant Accounting Policies Depreciation and Amortization (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Provision for Depreciation Rate	2.70%	2.70%
Projected provision for depreciation in next fiscal year	2.70%
Percent Of Intangible Plant Balance Amortizable	98.90%
Percent of Intangible Plant Balance Amortizable Thereafter	1.10%
Transmission Equipment [Member] | OG&E [Member]
Amount of Acquisition Adjustments	$ 3.3
Redbud Plant [Member]
Amount of Acquisition Adjustments	$ 148.3	$ 148.3

Summary of Significant Accou_10

Summary of Significant Accounting Policies Asset Retirement Obligation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1		$ 83.9	$ 75.1
Accretion expense		1	3.4
Revisions in estimated cash flows	[1]	(2.4)	6.8
Liabilities settled	[2]	(9)	(1.4)
Balance at December 31		$ 73.5	$ 83.9
[1]	Assumptions changed related to the estimated cost of the removal of wind turbine assets and asbestos removal at OG&E's generating facilities.
[2]	Asset retirement obligations were settled for asbestos removal and for the closure of an ash pond at OG&E's generating facilities.

Summary of Significant Accou_11

Summary of Significant Accounting Policies Enviromental Costs (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accrued Environmental Loss Contingencies, Noncurrent	$ 18.7	$ 23.4

Summary of Significant Accou_12

Summary of Significant Accounting Policies Allowance for Funds Used During Construction (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Public Utilities, Allowance for Funds Used During Construction, Rate	7.60%	7.60%	8.20%

Summary of Significant Accou_13

Summary of Significant Accounting Policies Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive (income) loss		$ (27.9)	$ (28.9)	$ (23.2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(9.1)	(12)
Amounts reclassified from accumulated other comprehensive income (loss)		(3.4)	(3.3)	(2.5)
Amounts reclassified from accumulated other comprehensive income (loss)		1.5	1.6
Net current period other comprehensive income (loss)		1	(5.7)
Amounts Reclassified from Accumulated OCI, Net of Tax and Noncontrolling Interest		10.1	6.3
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		(1.7)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		(12)	(8)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	[1]	(4.5)	(4.4)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	[1]	(11.3)	(6.3)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		(15.8)	(10.7)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		(3.8)	(2.7)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		1.9	1.7
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	[1]	0.2	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	[1]	2.3	2.3
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		2.5	2.3
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		0.6	0.6
Defined Benefit Plans Income Loss [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)		(35.1)	(38.8)	(32.7)
Other comprehensive income before reclassifications		(8.3)	(14.1)
Amounts reclassified from accumulated other comprehensive income (loss)		3.4	3.3
Net current period other comprehensive income (loss)		3.7	(6.1)
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		(4.2)
Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)		4.2	4.6	2.5
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(0.2)	2.1
Amounts reclassified from accumulated other comprehensive income (loss)		(0.2)	0
Net current period other comprehensive income (loss)		(0.4)	2.1
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		0.2
Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)		3.6	5.3	7
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		0	0
Amounts reclassified from accumulated other comprehensive income (loss)		(1.7)	(1.7)
Net current period other comprehensive income (loss)		(1.7)	(1.7)
Components of Net Periodic Benefit Costs to be Recognized in Next Fiscal Year		2.3
Settlement Cost [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		8.6	4.7
Settlement Cost [Member] | Defined Benefit Plans Income Loss [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		8.6	4.7
Settlement Cost [Member] | Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		0	0
Settlement Cost [Member] | Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)		0	0
Commodity Contract [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive income (loss)			(0.6)	$ 0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0
Amounts reclassified from accumulated other comprehensive income (loss)		0	0
Amounts reclassified from accumulated other comprehensive income (loss)		(0.6)	0
Net current period other comprehensive income (loss)		(0.6)	0
Amounts removed from accumulated other comprehensive income due to deconsolidation		$ 0	$ 0
[1]	These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost (see Note 13 for additional information).

Accounting Pronouncements New A

Accounting Pronouncements New Accounting Pronouncement (Details) - USD ($) $ in Millions	Dec. 31, 2019		Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 40.9	[1]	$ 34.5
Operating Lease, Liability	$ 45.8	[2]	$ 39.1
[1]	Included in Property, Plant and Equipment in the 2019 Consolidated Balance Sheet.
[2]	Included in Other Deferred Credits and Other Liabilities in the 2019 Consolidated Balance Sheet.

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,175.5	$ 2,211.7	$ 0
Provision for Rate Refund [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	(0.9)	(6)
Integrated Market [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	38.4	48.7
Transmission [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	148	147.4
Other Contracts with Customers [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	29.1	27.1
Residential [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	865.8	877.8
Commercial [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	486.6	500
Industrial [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	217.8	228.9
Oilfield [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	200.4	190.4
Public Authority [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	190.3	197.4
Total Retail Customer [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 1,960.9	$ 1,994.5

Leases, Codification Topic 84_2

Leases, Codification Topic 842 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Jan. 01, 2019
Leases [Abstract]
Lessee, Operating Lease, Contingent Liability	$ 6.8		$ 16.2
Operating Lease, Cost	6		4.9		$ 6.2
Operating Leased Assets [Line Items]
Cash Paid on Operating Leases	5.6
Operating Lease, Right-of-Use Asset	40.9	[1]				$ 34.5
Operating Lease, Liability	$ 45.8	[2]				$ 39.1
Operating Lease, Weighted Average Remaining Lease Term	13 years 1 month 6 days
Operating Lease, Weighted Average Discount Rate, Percent	3.90%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 10.7
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	0		22.1	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	6.2		3.9	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Two	5.8		3.5	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Three	5.2		2.9	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Four	5.2		2.9	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Five	3.1		3	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due after Year Five	34.7		34.6	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due	60.2		72.9	[3],[4]
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	14.4
Lessee, Operating Lease, Contingent Liability	$ 6.8		$ 16.2
[1]	Included in Property, Plant and Equipment in the 2019 Consolidated Balance Sheet.
[2]	Included in Other Deferred Credits and Other Liabilities in the 2019 Consolidated Balance Sheet.
[3]	Amounts included for comparability and accounted for in accordance with ASC 840, "Leases."
[4]	At the end of the railcar lease term, which was February 1, 2019, OG&E had the option to either purchase the railcars at a stipulated fair market value or renew the lease. OG&E renewed the lease effective February 1, 2019. If OG&E chose not to purchase the railcars or renew the lease agreement and the actual fair value of the railcars was less than the stipulated fair market value, OG&E would have been responsible for the difference in those values up to a maximum of $16.2 million.

Investment in Unconsolidated _3

Investment in Unconsolidated Affiliate and Related Party Transactions (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 01, 2013
Schedule of Equity Method Investments [Line Items]
Limited Partner Units Owned	111
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest	25.50%	25.60%	25.70%
Distribution Made to Limited Partner, Distributions Declared, Per Unit	$ 0.33050
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 652.5	$ 680.3
Equity in earnings of unconsolidated affiliates	113.9	152.8	$ 131.2
Enable Midstream Partners [Member]
Schedule of Equity Method Investments [Line Items]
Distributions received	$ 144	141.2	141.2
Enogex LLC [Member]
Schedule of Equity Method Investments [Line Items]
Increase in fair value of net assets				$ 2,200
OGE Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest	25.50%
OGE Energy [Member]
Schedule of Equity Method Investments [Line Items]
Percentage Share of Management Rights	50.00%
CenterPoint [Member]
Schedule of Equity Method Investments [Line Items]
Percentage Share of Management Rights	50.00%
Natural Gas Midstream Operations [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates	$ 113.9	$ 152.8	$ 131.2

Investment in Unconsolidated _4

Investment in Unconsolidated Affiliate and Related Party Transactions Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Expected Settlement Charge	$ 17.3
Og and E [Member] | Enable Midstream Partners [Member]
Related Party Transaction [Line Items]
Revenue from Related Parties	15.9	$ 16.3	$ 14
Operating Costs Charged [Member] | OGE Energy [Member] | Enable Midstream Partners [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	0.5	0.6	2.3
Natural Gas Transportation [Member] | Og and E [Member] | Enable Midstream Partners [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	41.2	37.9	35
Natural Gas Purchases [Member] | Og and E [Member] | Enable Midstream Partners [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	(6)	(3.2)	(2.1)
Employment Costs [Member] | OGE Energy [Member] | Enable Midstream Partners [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	23.2	27.5	$ 29.5
Excluding Fuel Purchases [Member]
Related Party Transaction [Line Items]
Accounts receivable - unconsolidated affiliates	$ 0.8	$ 1.7

Investment in Unconsolidated _5

Investment in Unconsolidated Affiliate and Related Party Transactions Summarized Balance Sheet Information of Equity Method Investment (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Summarized Financial Information of Equity Method Investment [Line Items]
Current assets	$ 389	$ 449
Non-current assets	11,877	11,995
Current liabilities	780	1,615
Non-current liabilities	$ 4,077	$ 3,211

Investment in Unconsolidated _6

Investment in Unconsolidated Affiliate and Related Party Transactions Summarized Income Statement of Equity Method Investment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investment, Summarized Financial Information, Revenue	$ 2,960	$ 3,431	$ 2,803
Equity Method Investment, Summarized Financial Information, Cost of Sales	1,279	1,819	1,381
Equity Method Investment, Summarized Financial Information, Operating Income	569	648	528
Net income	$ 360	$ 485.3	$ 400.3

Investment in Unconsolidated _7

Investment in Unconsolidated Affiliate and Related Party Transactions Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Enable net income		$ 360	$ 485.3	$ 400.3
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%	25.60%	25.70%
Proportionate Unconsolidated Affiliate Net Income		$ 91.8	$ 124.4	$ 102.7
OGE Energy's portion of Enable net income				102.7
Amortization of basis difference and dilution recognition	[1]	22.1	28.4	28.5
Equity in earnings of unconsolidated affiliates		113.9	152.8	131.2
Natural Gas Midstream Operations [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates		$ 113.9	$ 152.8	$ 131.2
OGE Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%
OGE Energy [Member]
Schedule of Equity Method Investments [Line Items]
Amortization of basis difference and dilution recognition	[2]	$ 27.8
[1]	Includes loss on dilution, net of proportional basis difference recognition.
[2]	Includes proportional basis difference recognition due to dilution.

Investment in Unconsolidated _8

Investment in Unconsolidated Affiliate and Related Party Transactions Reconciliation of Basis Difference (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Basis Difference [Line Items]
Amortization of basis difference	[1]	$ 22.1	$ 28.4	$ 28.5
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		652.5	$ 680.3
OGE Energy [Member]
Reconciliation of Basis Difference [Line Items]
Amortization of basis difference	[2]	$ 27.8
[1]	Includes loss on dilution, net of proportional basis difference recognition.
[2]	Includes proportional basis difference recognition due to dilution.

Fair Value Measurements Carryin

Fair Value Measurements Carrying and Fair Value Amounts (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt	$ 3,195.2	$ 3,146.9
OG&E Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt	3,050.3	3,001.9
Long-Term Debt, Fair Value	3,500.4	3,178.2
OG&E Industrial Authority Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt	135.4	135.4
Long-Term Debt, Fair Value	135.4	135.4
OG&E Tinker Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt	9.5	9.6
Long-Term Debt, Fair Value	10	$ 8.7
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 0

Stock Based Compensation (Detai

Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Authorized		7,400,000
Tax Benefit from Compensation Expense		$ 3.6		$ 3.4	$ 3.5
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Minimum payout range		0.00%
Maximum payout range		200.00%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Total Compensation Cost Not yet Recognized		$ 11
Performance Units Related to Earnings Per Share [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		0	[1]	87,308	86,857
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 0		$ 31.03	$ 34.83
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number		155,171		251,825
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		0	[1]	87,308	86,857
Equity Instruments Other than Options, Converted in Period	[2]	(91,356)
Equity Instruments Other than Options, Forfeited in Period		(5,298)
Awards Other than Options, Fully Vested		74,053
Equity Instruments Other than Options, Converted, Aggregrate Intrinsic Value		$ 7.2
Equity Instruments Other than Options, Vested in Period, Aggregate Intrinsic Value		6.6
Equity Instruments Other than Options, Outstanding, Aggregrate Intrinsic Value		11.5
Equity Instruments Other than Options, Fully Vested, Aggregrate Intrinsic Value		$ 4.7
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Instruments Other than Options, Nonvested, Number, Beginning Balance		160,469
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		0	[1]	87,308	86,857
Equity Instruments Other than Options, Vested in Period		(74,053)
Equity Instruments Other than Options, Forfeited in Period		(5,298)
Equity Instruments Other than Options, Nonvested, Number, Ending Balance		81,118		160,469
Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 31.03		$ 32.82
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		0		$ 31.03	$ 34.83
Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value		34.83
Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value		$ 32.07
Awards Other than Options, Vested and Expected to Vest, Outstanding	[3]	77,617
Fair Value of Vested Performance Units and Restricted Stock		$ 5.2		$ 4.9	$ 1.2
Total Compensation Cost Not yet Recognized		$ 0.8
Total Compensation Cost Not yet Recognized, Period for Recognition		1 year
Total Shareholder Return [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		208,647	[1]	261,916	260,570
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 47		$ 36.86	$ 41.77
Expected Dividend Rate		4.00%		3.60%	3.80%
Expected Volatility Rate		17.00%		19.00%	19.90%
Risk Free Interest Rate		2.47%		2.38%	1.44%
Expected Term		2 years 10 months 9 days		2 years 10 months 9 days	2 years 9 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number		664,817		755,480
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		208,647	[1]	261,916	260,570
Equity Instruments Other than Options, Converted in Period	[2]	(274,078)
Equity Instruments Other than Options, Forfeited in Period		(25,232)
Awards Other than Options, Fully Vested		222,163
Equity Instruments Other than Options, Converted, Aggregrate Intrinsic Value		$ 19.8
Equity Instruments Other than Options, Vested in Period, Aggregate Intrinsic Value		11.5
Equity Instruments Other than Options, Outstanding, Aggregrate Intrinsic Value		35.4
Equity Instruments Other than Options, Fully Vested, Aggregrate Intrinsic Value		$ 22.8
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Instruments Other than Options, Nonvested, Number, Beginning Balance		481,402
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		208,647	[1]	261,916	260,570
Equity Instruments Other than Options, Vested in Period		(222,163)
Equity Instruments Other than Options, Forfeited in Period		(25,232)
Equity Instruments Other than Options, Nonvested, Number, Ending Balance		442,654		481,402
Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 41.43		$ 39.17
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		47		$ 36.86	$ 41.77
Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value		41.76
Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value		$ 41.45
Awards Other than Options, Vested and Expected to Vest, Outstanding	[3]	418,331
Fair Value of Vested Performance Units and Restricted Stock		$ 9.3		$ 5.9	$ 6.3
Total Compensation Cost Not yet Recognized		$ 8.7
Total Compensation Cost Not yet Recognized, Period for Recognition		1 year 8 months 1 day
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense		$ 13		13.3	9
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Total Compensation Cost Not yet Recognized		9.5
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense		$ 0.9		$ 0.1	$ 0.1
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		75,929		826	3,145
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 41.71		$ 36.28	$ 34.96
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number		72,880		2,711
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		75,929		826	3,145
Equity Instruments Other than Options, Forfeited in Period		(3,599)
Equity Instruments Other than Options, Vested in Period, Aggregate Intrinsic Value		$ 0.1
Equity Instruments Other than Options, Outstanding, Aggregrate Intrinsic Value		3.2
Equity Instruments Other than Options, Fully Vested, Aggregrate Intrinsic Value		$ 2.4
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Instruments Other than Options, Nonvested, Number, Beginning Balance		2,711
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		75,929		826	3,145
Equity Instruments Other than Options, Vested in Period		(2,161)
Equity Instruments Other than Options, Forfeited in Period		(3,599)
Equity Instruments Other than Options, Nonvested, Number, Ending Balance		72,880		2,711
Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 41.66		$ 35
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		41.71		$ 36.28	$ 34.96
Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value		34.66
Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value		$ 41.78
Awards Other than Options, Vested and Expected to Vest, Outstanding	[3]	54,102
Fair Value of Vested Performance Units and Restricted Stock		$ 0.1		$ 0.1	$ 0.1
Total Compensation Cost Not yet Recognized		$ 1.5
Total Compensation Cost Not yet Recognized, Period for Recognition		1 year 11 months 23 days
Stock Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense, Net of Unconsolidated Affiliates		$ 13.9		13.4	9.1
Performance Units Related to Earnings Per Share [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense		4.3		5.1	1.4
Total Shareholder Return [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense		$ 8.7		$ 8.2	$ 7.6
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		443,900		26,211	2,298
[1]	For performance units, this represents the target number of performance units granted. Actual number of performance units earned, if any, is dependent upon performance and may range from zero percent to 200 percent of the target.
[2]	These amounts represent performance units that vested at December 31, 2018 which were settled in February 2019.
[3]	The intrinsic value of the performance units based on total shareholder return and earnings per share is $22.8 million and $4.7 million, respectively. The intrinsic value of restricted stock units is $2.4 million.

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
NON-CASH INVESTING AND FINANCING ACTIVITIES
Power plant long-term service agreement		$ 28.9	$ (9.2)	$ (2.6)
SUPPLEMENTAL CASH FLOW INFORMATION
Interest (net of interest capitalized)	[1]	152.2	153.8	139.6
Income taxes (net of income tax refunds)		5.5	2.8	(16)
Interest costs capitalized		$ 2.8	$ 11.7	$ 18
[1]	Net of interest capitalized of $2.8 million, $11.7 million and $18.0 million in 2019, 2018 and 2017, respectively.

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Regulatory Liability, Noncurrent		$ 1,223.5	$ 1,270.7
Current Federal Tax Expense (Benefit)		(6.4)	(1.9)	$ 4.9
Current State and Local Tax Expense (Benefit)		5.1	(4.4)	(4.2)
Current Income Tax Expense (Benefit)		(1.3)	(6.3)	0.7
Deferred Federal Income Tax Expense (Benefit)		48.5	74.7	(75.9)
Deferred State and Local Income Tax Expense (Benefit)		(17.4)	3.7	26
Deferred Income Tax Expense (Benefit)		31.1	78.4	(49.9)
Investment Tax Credit		0	0.1	(0.1)
Income Tax Expense (Benefit)		$ 29.8	$ 72.2	$ (49.3)	[1]
Statutory federal tax rate		21.00%	21.00%	35.00%
Federal deferred tax revaluation		0.00%	0.40%	(41.20%)
Federal renewable energy credit (A)	[2]	(6.00%)	(5.10%)	(4.80%)
Remeasurement of state deferred tax liabilities		(0.80%)	(0.40%)	0.40%
401(k) dividends		(0.40%)	(0.30%)	(0.50%)
Federal investment tax credits, net		0.00%	0.00%	(0.10%)
State income taxes, net of federal income tax benefit		(1.20%)	0.40%	2.00%
Effective Income Tax Rate Reconciliation, Executive Compensation Limitation, Percent		0.20%	0.20%	0.00%
Amortization of net unfunded deferred taxes		(4.50%)	(2.10%)	0.70%
Other		(0.70%)	0.40%	(0.10%)
Effective income tax rate		6.40%	14.50%	(8.60%)
Accrued liabilities		$ (10.7)	$ (12.5)
Accrued vacation		(2.1)	(2.3)
Uncollectible accounts		(0.4)	(0.4)
Accelerated depreciation and other property related differences		1,656.8	1,605.3
Investment in Enable		478.2	469.9
Regulatory assets		28.4	17.4
Income taxes recoverable from customers, net		(229.9)	(239.6)
Company Pension Plan		4.1	7.6
Bond redemption-unamortized costs		2.2	2.4
Derivative instruments		1.6	1.7
Federal tax credits		(238)	(237.8)
State tax credits		(185.8)	(156)
Postretirement medical and life insurance benefits		(23.3)	(23.6)
Net operating losses		(16.6)	(20.2)
Regulatory liabilities		(68.1)	(78.8)
Asset retirement obligations		(19.2)	(21.5)
Deferred federal investment tax credits		(1.8)	(1.8)
Other		0.4	1.1
Total deferred income tax liabilities, net		1,375.8	1,310.9
Unrecognized Tax Benefits		20.7	20.7	$ 20.7		$ 20.7
Current year additions		0	0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		0
Tax Credit Carryforward, Deferred Tax Asset		$ 238	$ 237.8
Stock-based compensation		(1.20%)	0.00%	0.00%
State operating loss [Member]
Operating Loss Carryforwards		$ 371.6
Deferred Tax Assets, Operating Loss Carryforwards, State and Local		16.6
Federal tax credits [Member]
Federal tax credits		(238)
Tax Credit Carryforward, Amount		238
Tax Credit Carryforward, Deferred Tax Asset		238
Oklahoma investment tax credits [Member]
State tax credits		(145.3)
Tax Credit Carryforward, Amount		183.9
Oklahoma capital investment board credits [Member]
State tax credits		(12.4)
Tax Credit Carryforward, Amount		12.4
Oklahoma zero emission tax credits [Member]
State tax credits		(28)
Tax Credit Carryforward, Amount		34.9
Louisiana inventory credits
State tax credits		(0.1)
Tax Credit Carryforward, Amount		0.2
Og and E [Member]
Unrecognized Tax Benefits		$ 16.4	$ 16.4	$ 16.4
[1]	The Company recorded an income tax benefit of $245.2 million and income tax expense of $10.5 million during the fourth quarter of 2017 due to the Company remeasuring deferred taxes related to the natural gas midstream operations and other operations segments, respectively, as a result of the 2017 Tax Act.
[2]	Represents credits associated with the production from OG&E's wind farms.

Common Equity Automatic Dividen

Common Equity Automatic Dividend Reinvestment and Stock Purchase Plan (Details) - Automatic Dividend Reinvestment and Stock Purchase Plan [Member]	12 Months Ended
	Dec. 31, 2019shares
Stock Issued During Period, Shares, Dividend Reinvestment Plan and Stock Purchase Plan	0
Shares Held in Reserve Related to Dividend Reinvestment Plan and Stock Purchase Plan	4,774,442

Common Equity Earnings Per Shar

Common Equity Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount																	0		0		0
Net income attributable to OGE Energy	$ 35.4		$ 250.9		$ 100.2		$ 47.1		$ 54.7		$ 205.1		$ 110.7		$ 55		$ 433.6		$ 425.5		$ 619
Basic Average Common Shares Outstanding																	200.1		199.7		199.7
Contingently Issuable Shares (Performance and Restricted Stock Units)																	0.6		0.8		0.3
Diluted Average Common Shares Outstanding																	200.7		200.5		200
Earnings Per Share, Basic and Diluted [Abstract]
Basic earnings per average common share attributable to OGE Energy common shareholders	$ 0.18	[1]	$ 1.25	[1]	$ 0.50	[1]	$ 0.24	[1]	$ 0.27	[1]	$ 1.03	[1]	$ 0.55	[1]	$ 0.28	[1]	$ 2.17	[1]	$ 2.13	[1]	$ 3.10
Diluted earnings per average common share attributable to OGE Energy common shareholders	$ 0.18	[1]	$ 1.25	[1]	$ 0.50	[1]	$ 0.24	[1]	$ 0.27	[1]	$ 1.02	[1]	$ 0.55	[1]	$ 0.27	[1]	$ 2.16	[1]	$ 2.12	[1]	$ 3.10
Retained Earnings [Member]
Net income attributable to OGE Energy																	$ 433.6		$ 425.5		$ 619
[1]	Due to the impact of dilution on the earnings per share calculation, quarterly earnings per share amounts may not add to the total.

Common Equity Dividends Restric

Common Equity Dividends Restriction (Details) shares in Millions, $ in Millions	Dec. 31, 2019USD ($)shares
Preferred Stock, Shares Outstanding | shares	0
OGE Energy [Member]
Ratio of Consolidated Debt to Consolidated Capitalization	65.00%
Retained Earnings, Restricted	$ 661.4
Retained Earnings, Unrestricted	$ 2,400
Og and E [Member]
Ratio of Consolidated Debt to Consolidated Capitalization	65.00%
Retained Earnings, Restricted	$ 694.9
Retained Earnings, Unrestricted	$ 2,200

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total long-term debt	$ 3,195.2	$ 3,146.9
Percent of Principal Amount Subject to Optional Tender	100.00%
Date Due	Mar. 15, 2030
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Debt Instrument, Face Amount	$ 300
Garfield Industrial Authority, January 1, 2025 [Member]
Debt Instrument [Line Items]
Date Due	Jan. 1, 2025
Muskogee Industrial Authority, Janaury 1, 2025 [Member]
Debt Instrument [Line Items]
Date Due	Jan. 1, 2025
Muskogee Industrial Authority, June 1, 2027 [Member]
Debt Instrument [Line Items]
Date Due	Jun. 1, 2027
Redeemable during the next 12 months
Debt Instrument [Line Items]
Total long-term debt	$ 135.4
OG&E [Member] | Redeemable during the next 12 months | Garfield Industrial Authority, January 1, 2025 [Member]
Debt Instrument [Line Items]
Long term debt, gross	47	47
OG&E [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority, Janaury 1, 2025 [Member]
Debt Instrument [Line Items]
Long term debt, gross	32.4	32.4
OG&E [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority, June 1, 2027 [Member]
Debt Instrument [Line Items]
Long term debt, gross	56	56
Senior Notes [Member] | OG&E [Member] | Series Due March 15, 2030
Debt Instrument [Line Items]
Long term debt, gross	$ 300	$ 0
Debt Instrument, Interest Rate, Stated Percentage	3.30%
Date Due	Mar. 15, 2030
Minimum [Member] | Redeemable during the next 12 months | Garfield Industrial Authority, January 1, 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.20%
Minimum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority, Janaury 1, 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.19%
Minimum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority, June 1, 2027 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.20%
Maximum [Member] | Redeemable during the next 12 months | Garfield Industrial Authority, January 1, 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.50%
Maximum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority, Janaury 1, 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.35%
Maximum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority, June 1, 2027 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.48%

Short-Term Debt and Credit Fa_3

Short-Term Debt and Credit Facilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Short-term debt		$ 112	$ 0
Line of Credit Facility [Abstract]
Aggregate Commitment		900
Amount Outstanding	[1]	$ 112.3
Weighted Average Interest Rate		2.06%
OGE Energy [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	[2]	$ 450
Line of Credit Facility [Abstract]
Amount Outstanding	[1],[2]	$ 112
Weighted Average Interest Rate	[2],[3]	2.06%
Maturity		Mar. 8, 2023
Ratio of Consolidated Debt to Consolidated Capitalization		65.00%
OG&E [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	[4]	$ 450
Line of Credit Facility [Abstract]
Letters of Credit Outstanding, Amount	[1],[4]	$ 0.3
Weighted Average Interest Rate	[3],[4]	1.00%
Maturity		Mar. 8, 2023
Period For Which Regulatory Approval Has Been Given to Acquire Short Term Debt		2 years
Short Term Borrowing Capacity That Has Regulatory Approval		$ 800
Ratio of Consolidated Debt to Consolidated Capitalization		65.00%
Uninsured Judgements [Member] | OGE Energy [Member]
Line of Credit Facility [Abstract]
Acceleration of Indebtedness of Credit Facility		$ 100
Uninsured Judgements [Member] | OG&E [Member]
Line of Credit Facility [Abstract]
Acceleration of Indebtedness of Credit Facility		$ 100
[1]	Includes direct borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit at December 31, 2019.
[2]	This bank facility is available to back up the Company's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility.
[3]	Represents the weighted-average interest rate for the outstanding borrowings under the revolving credit agreements, commercial paper borrowings and letters of credit.
[4]	This bank facility is available to back up OG&E's commercial paper borrowings and to provide revolving credit borrowings. This bank facility can also be used as a letter of credit facility.

Retirement Plans and Postreti_3

Retirement Plans and Postretirement Benefit Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match		200.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		5.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions		$ 20		$ 15
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Effect of One Percentage Point Increase on Service and Interest Cost Components		0		0		$ 0
Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation		0.1		0.1		0.1
Effect of One Percentage Point Decrease on Service and Interest Cost Components		0		0		0
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation		0.3		0.3		0.3
Expected Future Benefit Payments, Next Twelve Months		58.4
Expected Future Benefit Payments, Year Two		56.8
Expected Future Benefit Payments, Year Three		56.2
Expected Future Benefit Payments, Year Four		55.7
Expected Future Benefit Payments, Year Five		56.6
Expected Future Benefit Payments, Five Fiscal Years Thereafter		249.4
Defined Contribution Plan, Cost		14.4		13.2		13.2
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Benefits Paid		(14.6)		(14.6)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0		0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		615.9		687.5
Service cost		12.9		14.9		15.5
Interest cost		20.7		23.8		26.2
Plan settlements		(83.1)		(73.7)
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		0		0
Actuarial losses (gains)		64.3		(22)
Benefit Obligation, Ending		616.1		615.9		687.5
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		522.8		635.3
Actual return on plans' assets		85.2		(39.2)
Employer contributions		20		15
Plan settlements		(83.1)		(73.7)
Fair Value of Plan Assets, Ending		530.3		522.8		635.3
Funded Status of Plan		(85.8)		(93.1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		12.9		14.9		15.5
Interest cost		20.7		23.8		26.2
Expected return on plan assets		(36.1)		(44.1)		(42.6)
Defined Benefit Plan, Amortization of Gain (Loss)		(17.3)		(16.2)		(17.4)
Amortization of unrecognized prior service cost	[1]	0		0		(0.1)
Settlement cost		27.6		25.1		15.3
Net periodic benefit cost		42.4		35.9		31.7
Amount paid by unconsolidated affiliates		2.9		2.5		4.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates		39.5		33.4		27.4
Plan settlements		(83.1)		(73.7)
Capitalized Portion of Net Periodic Benefit Cost		$ 3.6		$ 3.8		$ 4.4
Assumptions Used Calculating Benefit Obligation, Discount Rate		3.15%		4.20%		3.60%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		7.50%		7.50%		7.50%
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		4.20%		4.20%		4.20%
Fair Value of Plan Assets, Beginning		$ 522.8		$ 635.3
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		0		0
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(14.6)		(14.6)
Pension Plans, Defined Benefit [Member] | OKLAHOMA
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost	[2]	17.9		22.1		$ 13.2
Additional Pension Expense to Meet State Requirements	[2]	(16.1)		(14.1)		(2.3)
Pension Plans, Defined Benefit [Member] | ARKANSAS
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost	[2]	1.7		2.1		1.1
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Restoration of Retirement Income Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Benefits Paid		0		0
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0.3		0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		9.6		8.1
Service cost		0.5		0.4		0.3
Interest cost		0.4		0.3		0.3
Plan settlements		(1.2)		(2)
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		0		0
Actuarial losses (gains)		0.7		2.8
Benefit Obligation, Ending		10.3		9.6		8.1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0		0
Actual return on plans' assets		0		0
Employer contributions		1.2		2
Plan settlements		(1.2)		(2)
Fair Value of Plan Assets, Ending		0		0		0
Funded Status of Plan		(10.3)		(9.6)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.5		0.4		0.3
Interest cost		0.4		0.3		0.3
Expected return on plan assets		0		0		0
Defined Benefit Plan, Amortization of Gain (Loss)		(0.5)		(0.7)		(0.4)
Amortization of unrecognized prior service cost	[1]	0		0.1		0.1
Settlement cost		0.5		1		0
Net periodic benefit cost		1.9		2.5		1.1
Amount paid by unconsolidated affiliates		0.1		0.1		0
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates		1.8		2.4		1.1
Plan settlements		(1.2)		(2)
Fair Value of Plan Assets, Beginning		0		0
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		0		0
Defined Benefit Plan, Benefit Obligation, Benefits Paid		0		0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Benefits Paid		(12.1)		(13.5)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0		0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		135.8		149.4
Service cost		0.2		0.3		0.6
Interest cost		5.6		5.4		7.2
Plan settlements		0		0
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		(4.1)		(3.8)
Actuarial losses (gains)		2.9		(9.6)
Benefit Obligation, Ending		136.5		135.8		149.4
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		45.3		50.2
Actual return on plans' assets		4.6		(0.6)
Employer contributions		5.1		5.4
Plan settlements		0		0
Fair Value of Plan Assets, Ending		47		45.3		50.2
Funded Status of Plan		(89.5)		(90.5)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.2		0.3		0.6
Interest cost		5.6		5.4		7.2
Expected return on plan assets		(1.9)		(2)		(2.2)
Defined Benefit Plan, Amortization of Gain (Loss)		(2)		(3.8)		(2)
Amortization of unrecognized prior service cost	[1]	(8.4)		(8.4)		(3.5)
Settlement cost		0		0		0.6
Net periodic benefit cost		(2.5)		(0.9)		4.7
Amount paid by unconsolidated affiliates		(0.6)		(0.5)		0.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates		(1.9)		(0.4)		4.4
Plan settlements		0		0
Capitalized Portion of Net Periodic Benefit Cost		$ 0.2		$ 0.2		$ 1.2
Assumptions Used Calculating Benefit Obligation, Discount Rate		3.25%		4.30%		3.70%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		4.00%		4.00%		4.00%
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase						4.20%
Health Care Cost Trend Rate Assumed for Next Fiscal Year				7.00%
Fair Value of Plan Assets, Beginning		$ 45.3		$ 50.2
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		4.1		3.8
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(12.1)		(13.5)
Other Postretirement Benefits Plan [Member] | OKLAHOMA
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Additional Pension Expense to Meet State Requirements	[3]	1		4.4		$ 6.2
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		9.8
Fair Value of Plan Assets, Ending		12.1		9.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		9.8
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		36
Fair Value of Plan Assets, Ending		34.8		36
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		36
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		45.8
Fair Value of Plan Assets, Ending		46.9		45.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		$ 45.8
Less Than 90% [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income		50.00%
Projected Benefit Obligation Funded Status Thresholds Equity		50.00%
Projected Benefit Obligation Funded Status Thresholds		100.00%
95% [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income		58.00%
Projected Benefit Obligation Funded Status Thresholds Equity		42.00%
Projected Benefit Obligation Funded Status Thresholds		100.00%
100% [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income		65.00%
Projected Benefit Obligation Funded Status Thresholds Equity		35.00%
Projected Benefit Obligation Funded Status Thresholds		100.00%
105% [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income		73.00%
Projected Benefit Obligation Funded Status Thresholds Equity		27.00%
Projected Benefit Obligation Funded Status Thresholds		100.00%
110% [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income		80.00%
Projected Benefit Obligation Funded Status Thresholds Equity		20.00%
Projected Benefit Obligation Funded Status Thresholds		100.00%
115% [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income		85.00%
Projected Benefit Obligation Funded Status Thresholds Equity		15.00%
Projected Benefit Obligation Funded Status Thresholds		100.00%
120% [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Projected Benefit Obligation Funded Status Thresholds Fixed Income		90.00%
Projected Benefit Obligation Funded Status Thresholds Equity		10.00%
Projected Benefit Obligation Funded Status Thresholds		100.00%
Domestic All-Cap/Large Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		40.00%
Domestic Mid-Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		15.00%
Domestic Small-Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		25.00%
International Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		20.00%
Minimum [Member] | Domestic All-Cap/Large Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		35.00%
Minimum [Member] | Domestic Mid-Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		5.00%
Minimum [Member] | Domestic Small-Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		5.00%
Minimum [Member] | International Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		10.00%
Maximum [Member] | Domestic All-Cap/Large Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		60.00%
Maximum [Member] | Domestic Mid-Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		25.00%
Maximum [Member] | Domestic Small-Cap Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		30.00%
Maximum [Member] | International Equity [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Target Plan Asset Allocations		30.00%
Group Retiree Medical Insurance Contract [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		$ 36
Fair Value of Plan Assets, Ending		34.8		36
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		36
Group Retiree Medical Insurance Contract [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Group Retiree Medical Insurance Contract [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		36
Fair Value of Plan Assets, Ending		34.8		36
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		36
U.S. common stocks [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		169.3
Fair Value of Plan Assets, Ending		202		169.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		169.3
U.S. common stocks [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		169.3
Fair Value of Plan Assets, Ending		202		169.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		169.3
U.S. common stocks [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
U.S. treasury notes and bonds [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4],[6]	0	[5],[7]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[7]	137.9
Fair Value of Plan Assets, Ending	[7]	134.8		137.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[7]	137.9
U.S. treasury notes and bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[7]	137.9
Fair Value of Plan Assets, Ending	[7]	134.8		137.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[7]	137.9
U.S. treasury notes and bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[7]	0
Fair Value of Plan Assets, Ending	[7]	0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[7]	0
Mortgage-backed securities | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		65.9
Fair Value of Plan Assets, Ending		45.8		65.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		65.9
Mortgage-backed securities | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Mortgage-backed securities | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		65.9
Fair Value of Plan Assets, Ending		45.8		65.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		65.9
Corporate fixed income and other securities [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		143.2
Fair Value of Plan Assets, Ending		130.5		143.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		143.2
Corporate fixed income and other securities [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Corporate fixed income and other securities [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		143.2
Fair Value of Plan Assets, Ending		130.5		143.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		143.2
Commingled fund [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		23.9	[4],[8]	19.7	[5],[9]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[9]	19.7
Fair Value of Plan Assets, Ending	[9]	23.9		19.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[9]	19.7
Commingled fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[9]	0
Fair Value of Plan Assets, Ending	[9]	0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[9]	0
Commingled fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[9]	0
Fair Value of Plan Assets, Ending	[9]	0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[9]	0
Foreign government bonds [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		4.4
Fair Value of Plan Assets, Ending		3		4.4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		4.4
Foreign government bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Foreign government bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		4.4
Fair Value of Plan Assets, Ending		3		4.4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		4.4
Municipal bonds [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.6
Fair Value of Plan Assets, Ending		1.1		0.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.6
Municipal bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Municipal bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.6
Fair Value of Plan Assets, Ending		1.1		0.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.6
Money market funds [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		7.5	[4]	0.3	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.3
Fair Value of Plan Assets, Ending		7.5		0.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.3
Money market funds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Money market funds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Money market funds [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		1.2
Money market funds [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		1.2
Money market funds [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		0
Mutual fund [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		8
Fair Value of Plan Assets, Ending		2.4		8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		8
Mutual fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		8
Fair Value of Plan Assets, Ending		2.4		8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		8
Mutual fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		27
Fair Value of Plan Assets, Ending		22.9		27
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		27
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		27
Fair Value of Plan Assets, Ending		22.9		27
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		27
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		(20.4)
Fair Value of Plan Assets, Ending		(10.9)		(20.4)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		(20.4)
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		(20.4)
Fair Value of Plan Assets, Ending		(10.9)		(20.4)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		(20.4)
Cash collateral [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.7
Fair Value of Plan Assets, Ending		0.6		0.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.7
Cash collateral [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.7
Fair Value of Plan Assets, Ending		0.6		0.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.7
Cash collateral [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Receivable (foreign currency) [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0	[4]	0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.1
Fair Value of Plan Assets, Ending		0.1		0.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.1
Receivable (foreign currency) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0
Receivable (foreign currency) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.1
Fair Value of Plan Assets, Ending		0.1		0.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.1
Preferred stocks (foreign) [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment	[4]	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		0.7
Preferred stocks (foreign) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		0.7
Preferred stocks (foreign) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		0
Total Plan investments [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		31.4	[4]	20	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		556.7
Fair Value of Plan Assets, Ending		564.4		556.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		556.7
Total Plan investments [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		315.9
Fair Value of Plan Assets, Ending		340.5		315.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		315.9
Total Plan investments [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		220.8
Fair Value of Plan Assets, Ending		192.5		220.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		220.8
Interest and dividends receivable [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		3
Fair Value of Plan Assets, Ending		2.4		3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		3
Payable to broker for securities purchased [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		(36.9)
Fair Value of Plan Assets, Ending		(36.5)		(36.9)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		(36.9)
Total Plan assets [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		522.8
Fair Value of Plan Assets, Ending		530.3		$ 522.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		$ 522.8
[1]	Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment.
[2]	Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.
[3]	Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.
[4]	GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.
[5]	GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.
[6]	This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher.
[7]	This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher.
[8]	This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.
[9]	This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.

Retirement Plans and Postreti_4

Retirement Plans and Postretirement Benefit Plans Postretirement Benefit Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions		$ 20	$ 15
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Level 3 Asset Value, Beginning of Period		36
Interest income		0.8
Dividend income		0.5
Unrealized gains		1.4
Administrative expenses and charges		(0.1)
Claims paid		(3.8)
Level 3 Asset Value, End of Period		34.8	36
Postretirement Plan, Expected Future Benefit Payments, Next Twelve Months					$ 11.2
Postretirement Plan, Expected Future Benefit Payments, Year Two					11.2
Postretirement Plan, Expected Future Benefit Payments, Year Three					11.1
Postretirement Plan, Expected Future Benefit Payments in Year Four					9.5
Postretirement Plan, Expected Future Benefit Payments, Year Five					9.4
Postretirement Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter					42.3
Postemployment Benefits Liability					2.1		$ 1.9
Defined Contribution Plan, Cost		$ 14.4	13.2	$ 13.2
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay		5.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match		200.00%
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 34.8	36		34.8		36
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Claims Paid		3.8
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Administrative Expenses and Charges		0.1
Unrealized gains		1.4
Interest income		0.8
Dividend income		0.5
Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.9
Fair Value of Plan Assets, Ending			0.9
Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.9
Fair Value of Plan Assets, Ending			0.9
Fair Value, Inputs, Level 3 [Member] | Cash [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending			0
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		615.9	687.5
Service cost		12.9	14.9	15.5
Interest cost		20.7	23.8	26.2
Plan settlements		(83.1)	(73.7)
Actuarial losses (gains)		64.3	(22)
Benefit Obligation, Ending		616.1	615.9	687.5
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		522.8	635.3
Actual return on plans' assets		85.2	(39.2)
Employer contributions		20	15
Plan settlements		(83.1)	(73.7)
Fair Value of Plan Assets, Ending		530.3	522.8	635.3
Funded Status of Plan					$ (85.8)		$ (93.1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		12.9	14.9	15.5
Interest cost		20.7	23.8	26.2
Expected return on plan assets		(36.1)	(44.1)	(42.6)
Amortization of unrecognized prior service cost	[1]	0	0	(0.1)
Settlement cost		27.6	25.1	15.3
Net periodic benefit cost		42.4	35.9	31.7
Amount paid by unconsolidated affiliates		2.9	2.5	4.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates		39.5	33.4	27.4
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Capitalized Portion of Net Periodic Benefit Cost		$ 3.6	$ 3.8	$ 4.4
Assumptions Used Calculating Benefit Obligation, Discount Rate				3.60%	3.15%		4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.63%	3.73%	4.00%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		7.50%	7.50%	7.50%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase				4.20%	4.20%		4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		4.20%	4.20%	4.20%
Defined Benefit Plan, Benefit Obligation, Benefits Paid		$ (14.6)	$ (14.6)
Defined Benefit Plan, Plan Assets, Benefits Paid		14.6	14.6
Accumulated Benefit Obligation					$ 563.3		$ 561.9
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0	0
Pension Plan [Member] | Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[2]	19.7
Fair Value of Plan Assets, Ending	[2]	23.9	19.7
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Alternative Investment					23.9	[3],[4]	19.7	[2],[5]
Pension Plan [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0.3
Fair Value of Plan Assets, Ending		7.5	0.3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Alternative Investment					7.5	[3]	0.3	[5]
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[2]	0
Fair Value of Plan Assets, Ending	[2]	0	0
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0	0
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning	[2]	0
Fair Value of Plan Assets, Ending	[2]	0	0
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0	0
Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0	0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		135.8	149.4
Service cost		0.2	0.3	$ 0.6
Interest cost		5.6	5.4	7.2
Plan settlements		0	0
Actuarial losses (gains)		2.9	(9.6)
Benefit Obligation, Ending		136.5	135.8	149.4
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		45.3	50.2
Actual return on plans' assets		4.6	(0.6)
Employer contributions		5.1	5.4
Plan settlements		0	0
Fair Value of Plan Assets, Ending		47	45.3	50.2
Funded Status of Plan					$ (89.5)		$ (90.5)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.2	0.3	0.6
Interest cost		5.6	5.4	7.2
Expected return on plan assets		(1.9)	(2)	(2.2)
Amortization of unrecognized prior service cost	[1]	(8.4)	(8.4)	(3.5)
Settlement cost		0	0	0.6
Net periodic benefit cost		(2.5)	(0.9)	4.7
Amount paid by unconsolidated affiliates		(0.6)	(0.5)	0.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates		(1.9)	(0.4)	4.4
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Capitalized Portion of Net Periodic Benefit Cost		$ 0.2	$ 0.2	$ 1.2
Assumptions Used Calculating Benefit Obligation, Discount Rate				3.70%	3.25%		4.30%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		4.30%	3.70%	4.20%
Health Care Cost Trend Rate Assumed for Next Fiscal Year							7.00%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		4.00%	4.00%	4.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				4.20%
Defined Benefit Plan, Benefit Obligation, Benefits Paid		$ (12.1)	$ (13.5)
Defined Benefit Plan, Plan Assets, Benefits Paid		12.1	13.5
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Group Retiree Medical Insurance Contract [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		36
Fair Value of Plan Assets, Ending		34.8	36
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Equity Mutual Funds Investment [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		8.9
Fair Value of Plan Assets, Ending		10.9	8.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		1.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		9.8
Fair Value of Plan Assets, Ending		12.1	9.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Group Retiree Medical Insurance Contract [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Equity Mutual Funds Investment [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		8.9
Fair Value of Plan Assets, Ending		10.9	8.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		1.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		36
Fair Value of Plan Assets, Ending		34.8	36
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Group Retiree Medical Insurance Contract [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		36
Fair Value of Plan Assets, Ending		34.8	36
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Equity Mutual Funds Investment [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0
Fair Value of Plan Assets, Ending		0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Money market funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Ending		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		45.8
Fair Value of Plan Assets, Ending		46.9	45.8
Other Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation, Beginning		9.6	8.1
Service cost		0.5	0.4	$ 0.3
Interest cost		0.4	0.3	0.3
Plan settlements		(1.2)	(2)
Actuarial losses (gains)		0.7	2.8
Benefit Obligation, Ending		10.3	9.6	8.1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		0	0
Actual return on plans' assets		0	0
Employer contributions		1.2	2
Plan settlements		(1.2)	(2)
Fair Value of Plan Assets, Ending		0	0	0
Funded Status of Plan					$ (10.3)		$ (9.6)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.5	0.4	0.3
Interest cost		0.4	0.3	0.3
Expected return on plan assets		0	0	0
Amortization of unrecognized prior service cost	[1]	0	0.1	0.1
Settlement cost		0.5	1	0
Net periodic benefit cost		1.9	2.5	1.1
Amount paid by unconsolidated affiliates		0.1	0.1	0
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates		1.8	2.4	1.1
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Benefits Paid		0	0
Defined Benefit Plan, Plan Assets, Benefits Paid		0	0
Accumulated Benefit Obligation					$ 8.1		$ 7.8
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0.3	0
OKLAHOMA | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost	[6]	$ 17.9	$ 22.1	$ 13.2
[1]	Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment.
[2]	This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.
[3]	GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.
[4]	This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.
[5]	GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.
[6]	Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.

Report of Business Segments (De

Report of Business Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 472.5	$ 755.4	$ 513.7	$ 490	$ 511.8	$ 698.8	$ 567	$ 492.7	$ 2,231.6	$ 2,270.3	$ 2,261.1
Cost of sales									786.9	892.5	897.6
Other operation and maintenance									491.8	474.6	458.7
Depreciation and amortization									355	321.6	283.5
Taxes other than income									93.6	92	89.4
Operating income (loss)	70.3	274.3	110	49.7	58	227.3	137.7	66.6	504.3	489.6	531.9
Equity in earnings of unconsolidated affiliates									113.9	152.8	131.2
Other income (expense)									(6.9)	11.3	50.4
Interest expense									147.9	156	143.8
Income tax expense (benefit)									29.8	72.2	(49.3)	[1]
NET INCOME	35.4	$ 250.9	$ 100.2	$ 47.1	54.7	$ 205.1	$ 110.7	$ 55	433.6	425.5	619
Investment in unconsolidated affiliates	1,151.5				1,177.5				1,151.5	1,177.5	1,160.4
Total assets	11,024.3				10,748.6				11,024.3	10,748.6	10,412.7
Capital expenditures									635.5	573.6	824.1
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,231.6	2,270.3	2,261.1
Cost of sales									786.9	892.5	897.6
Other operation and maintenance									492.5	473.8	469.8
Depreciation and amortization									355	321.6	280.9
Taxes other than income									89.5	88.2	84.8
Operating income (loss)									507.7	494.2	528
Equity in earnings of unconsolidated affiliates									0	0	0
Other income (expense)									3.1	25.6	57.7
Interest expense									140.5	151.8	138.4
Income tax expense (benefit)									20.1	40	141.8	[1]
NET INCOME									350.2	328	305.5
Investment in unconsolidated affiliates	0				0				0	0	0
Total assets	10,076.6				9,704.5				10,076.6	9,704.5	9,255.6
Capital expenditures									635.5	573.6	824.1
Natural Gas Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Cost of sales									0	0	0
Other operation and maintenance									2.8	1.4	(0.8)
Depreciation and amortization									0	0	0
Taxes other than income									0.4	0.6	1
Operating income (loss)									(3.2)	(2)	(0.2)
Equity in earnings of unconsolidated affiliates									113.9	152.8	131.2
Other income (expense)									(8.6)	(4.9)	(1)
Interest expense									0	0	0
Income tax expense (benefit)									20.7	37.1	(195.2)	[1]
NET INCOME									81.4	108.8	325.2
Investment in unconsolidated affiliates	1,132.9				1,166.6				1,132.9	1,166.6	1,151.9
Total assets	1,135.4				1,169.8				1,135.4	1,169.8	1,155.3
Capital expenditures									0	0	0
Other Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Cost of sales									0	0	0
Other operation and maintenance									(3.5)	(0.6)	(10.3)
Depreciation and amortization									0	0	2.6
Taxes other than income									3.7	3.2	3.6
Operating income (loss)									(0.2)	(2.6)	4.1
Equity in earnings of unconsolidated affiliates									0	0	0
Other income (expense)									2.2	(3.4)	(5.4)
Interest expense									11	10.2	6.3
Income tax expense (benefit)									(11)	(4.9)	4.1	[1]
NET INCOME									2	(11.3)	(11.7)
Investment in unconsolidated affiliates	18.6				10.9				18.6	10.9	8.5
Total assets	107				184.8				107	184.8	109.1
Capital expenditures									0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Cost of sales									0	0	0
Other operation and maintenance									0	0	0
Depreciation and amortization									0	0	0
Taxes other than income									0	0	0
Operating income (loss)									0	0	0
Equity in earnings of unconsolidated affiliates									0	0	0
Other income (expense)									(3.6)	(6)	(0.9)
Interest expense									(3.6)	(6)	(0.9)
Income tax expense (benefit)									0	0	0	[1]
NET INCOME									0	0	0
Investment in unconsolidated affiliates	0				0				0	0	0
Total assets	$ (294.7)				$ (310.5)				(294.7)	(310.5)	(107.3)
Capital expenditures									$ 0	$ 0	0
Tax Benefit Due to Tax Law Change [Member]
Segment Reporting Information [Line Items]
Income tax expense (benefit)											245.2
Tax Expense Due to Tax Law Change [Member]
Segment Reporting Information [Line Items]
Income tax expense (benefit)											$ 10.5
[1]	The Company recorded an income tax benefit of $245.2 million and income tax expense of $10.5 million during the fourth quarter of 2017 due to the Company remeasuring deferred taxes related to the natural gas midstream operations and other operations segments, respectively, as a result of the 2017 Tax Act.

Commitments and Contingencies_2

Commitments and Contingencies (Details) $ in Millions		12 Months Ended
		Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		$ 141.1
Operating Leases, Future Minimum Payments, Due in Two Years		113.5
Operating Leases, Future Minimum Payments, Due in Three Years		109.2
Operating Leases, Future Minimum Payments, Due in Four Years		121
Operating Leases, Future Minimum Payments, Due in Five Years		122.5
Operating Leases, Future Minimum Payments Due		607.3
Utilities Operating Expense, Purchased Power under Long-term Contracts		57.7	$ 57.6	$ 61.1
OG&E minimum fuel purchase commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		271.4
Purchase Obligation, Due in Next Twelve Months		82.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years		55.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years		50.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years		50.4
Unrecorded Unconditional Purchase Obligation, Due within Five Years		32.9
OG&E expected wind purchase commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		282.4
Purchase Obligation, Due in Next Twelve Months		55.7
Unrecorded Unconditional Purchase Obligation, Due within Two Years		56
Unrecorded Unconditional Purchase Obligation, Due within Three Years		56.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years		56.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years		57.5
OG&E long-term service agreement commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		53.1
Purchase Obligation, Due in Next Twelve Months		2.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years		2.4
Unrecorded Unconditional Purchase Obligation, Due within Three Years		2.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years		13.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years		32.1
Environmental compliance plan expenditures [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		0.4
Purchase Obligation, Due in Next Twelve Months		0.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years		0
Unrecorded Unconditional Purchase Obligation, Due within Three Years		0
Unrecorded Unconditional Purchase Obligation, Due within Four Years		0
Unrecorded Unconditional Purchase Obligation, Due within Five Years		0
OG&E total cogeneration payments [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount		14.7	112.4	115.2
OG&E capacity payments [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount		7.4	60	63
CPV Keenan [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		27.2	27	29
Edison Mission Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		23.1	21.7	22.1
FPL Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts	[1]	0	2.1	2.6
NextEra Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		$ 7.4	$ 6.8	$ 7.4
OG&E long-term service agreement commitments [Member] | McClain Plant [Member]
Loss Contingencies [Line Items]
Factored-Fired Hours		128,000
Factored-Fired Starts		4,800
OG&E long-term service agreement commitments [Member] | Redbud Plant [Member]
Loss Contingencies [Line Items]
Factored-Fired Hours		144,000
Factored-Fired Starts		4,500
Additional Factored-Fired Hours		24,000
[1]	OG&E's purchased power contract with FPL Energy for 50 MWs expired in 2018.

Rate Matters and Regulation (De

Rate Matters and Regulation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 5.2
Customer Refund Liability, Current		4.8	$ 0.3
Regulatory Assets, Current		48.7	18.5
Public Utilities, Amount Requested for Acquisition		53.5
Estimated Refund to SPP		13
Investment in Grid Enhancement		800
Impact to Company [Member]
Estimated Refund to SPP		5
Customer Impact [Member]
Estimated Refund to SPP		$ 8
Oklahoma Corporation Commission [Member]
OG&E's Jurisdictional Revenues		86.00%
Arkansas Public Service Commission [Member]
OG&E's Jurisdictional Revenues		8.00%
Federal Energy Regulatory Commission [Member]
OG&E's Jurisdictional Revenues		6.00%
OKLAHOMA
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 77.6
ARKANSAS
Public Utilities, Approved Rate Increase (Decrease), Amount		(3.3)
Oklahoma demand program rider under recovery [Member]
Regulatory Assets, Current	[1]	$ 0	$ 6.4
FERC [Member]
Recommended Common Equity Percentage		7.85%
Public Utilities, Approved Return on Equity, Percentage		10.60%
[1]	Included in Other Current Assets in the Consolidated Balance Sheets.

Quarterly Financial Data (Detai

Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Operating revenues	$ 472.5		$ 755.4		$ 513.7		$ 490		$ 511.8		$ 698.8		$ 567		$ 492.7		$ 2,231.6		$ 2,270.3		$ 2,261.1
Operating income	70.3		274.3		110		49.7		58		227.3		137.7		66.6		504.3		489.6		531.9
Net income	$ 35.4		$ 250.9		$ 100.2		$ 47.1		$ 54.7		$ 205.1		$ 110.7		$ 55		$ 433.6		$ 425.5		$ 619
Basic earnings per average common share attributable to OGE Energy common shareholders	$ 0.18	[1]	$ 1.25	[1]	$ 0.50	[1]	$ 0.24	[1]	$ 0.27	[1]	$ 1.03	[1]	$ 0.55	[1]	$ 0.28	[1]	$ 2.17	[1]	$ 2.13	[1]	$ 3.10
Diluted earnings per average common share attributable to OGE Energy common shareholders	$ 0.18	[1]	$ 1.25	[1]	$ 0.50	[1]	$ 0.24	[1]	$ 0.27	[1]	$ 1.02	[1]	$ 0.55	[1]	$ 0.27	[1]	$ 2.16	[1]	$ 2.12	[1]	$ 3.10
[1]	Due to the impact of dilution on the earnings per share calculation, quarterly earnings per share amounts may not add to the total.

Schedule II (Details)

Schedule II (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance		$ 1.7	$ 1.5	$ 1.5
Valuation Allowances and Reserves, Charged to Cost and Expense		2.2	3.4	2.6
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	[1]	2.4	3.2	2.6
Valuation Allowances and Reserves, Ending Balance		$ 1.5	$ 1.7	$ 1.5
[1]	Uncollectible accounts receivable written off, net of recoveries.