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		$ 20.0		$ 15.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Effect of One Percentage Point Increase on Service and Interest Cost Components		0.0		0.0		$ 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		0.0		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		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		0.0
Actuarial losses (gains)		64.3		(22.0)
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		20.0		15.0
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		0.0		(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		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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		0.0
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0.3		0.0
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)		(2.0)
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		0.0		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		0.0
Actual return on plans' assets		0.0		0.0
Employer contributions		1.2		2.0
Plan settlements		(1.2)		(2.0)
Fair Value of Plan Assets, Ending		0.0		0.0		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		0.0		0.0
Defined Benefit Plan, Amortization of Gain (Loss)		(0.5)		(0.7)		(0.4)
Amortization of unrecognized prior service cost	[1]	0.0		0.1		0.1
Settlement cost		0.5		1.0		0.0
Net periodic benefit cost		1.9		2.5		1.1
Amount paid by unconsolidated affiliates		0.1		0.1		0.0
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates		1.8		2.4		1.1
Plan settlements		(1.2)		(2.0)
Fair Value of Plan Assets, Beginning		0.0		0.0
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		0.0		0.0
Defined Benefit Plan, Benefit Obligation, Benefits Paid		0.0		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		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		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		0.0
Fair Value of Plan Assets, Ending		47.0		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)		(2.0)		(2.2)
Defined Benefit Plan, Amortization of Gain (Loss)		(2.0)		(3.8)		(2.0)
Amortization of unrecognized prior service cost	[1]	(8.4)		(8.4)		(3.5)
Settlement cost		0.0		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		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]	1.0		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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		36.0
Fair Value of Plan Assets, Ending		34.8		36.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		36.0
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		$ 36.0
Fair Value of Plan Assets, Ending		34.8		36.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		36.0
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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		36.0
Fair Value of Plan Assets, Ending		34.8		36.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		36.0
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		0.0	[4]	0.0	[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		202.0		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		202.0		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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		0.0	[4],[6]	0.0	[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]	0.0
Fair Value of Plan Assets, Ending	[7]	0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[7]	0.0
Mortgage-backed securities | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0.0	[4]	0.0	[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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		0.0	[4]	0.0	[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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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]	0.0
Fair Value of Plan Assets, Ending	[9]	0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[9]	0.0
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]	0.0
Fair Value of Plan Assets, Ending	[9]	0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning	[9]	0.0
Foreign government bonds [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0.0	[4]	0.0	[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		3.0		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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		3.0		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		0.0	[4]	0.0	[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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		0.0
Mutual fund [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0.0	[4]	0.0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		8.0
Fair Value of Plan Assets, Ending		2.4		8.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		8.0
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		8.0
Fair Value of Plan Assets, Ending		2.4		8.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		8.0
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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0.0	[4]	0.0	[5]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets, Beginning		27.0
Fair Value of Plan Assets, Ending		22.9		27.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		27.0
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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		27.0
Fair Value of Plan Assets, Ending		22.9		27.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		27.0
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0.0	[4]	0.0	[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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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		0.0	[4]	0.0	[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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
Receivable (foreign currency) [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment		0.0	[4]	0.0	[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		0.0
Fair Value of Plan Assets, Ending		0.0		0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		0.0
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]	0.0
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		0.0
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]	20.0	[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		3.0
Fair Value of Plan Assets, Ending		2.4		3.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Fair Value of Plan Assets, Beginning		3.0
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.