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Retirement Plans and Postretirement Benefit Plans (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Contribution Plan, Cost Recognized $ 14.2 $ 13.4 $ 12.3
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year 26.0    
Expected Future Benefit Payments, Next Twelve Months 93.2    
Expected Future Benefit Payments, Year Two 82.0    
Expected Future Benefit Payments, Year Three 76.7    
Expected Future Benefit Payments, Year Four 71.7    
Expected Future Benefit Payments, Year Five 64.7    
Expected Future Benefit Payments, Five Fiscal Years Thereafter 270.1    
Fair Value of Plan Assets 61.4 59.6  
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 0.1 0.1 0.1
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation 0.6 0.9 0.6
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Beginning 59.6    
Employer contributions 35.0 35.0  
Fair Value of Plan Assets, Ending 61.4 59.6  
Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 8.3 6.3  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 8.3 6.3  
Fair Value, Inputs, Level 3 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 53.1 53.3  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 53.1 53.3  
U.S. common stocks [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 236.8 232.2  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 236.8 232.2  
U.S. common stocks [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 236.8 232.2  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 236.8 232.2  
U.S. common stocks [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
Foreign common stocks [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 39.3 39.9  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 39.3 39.9  
Foreign common stocks [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 39.3 39.9  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 39.3 39.9  
Foreign common stocks [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
U.S. treasury notes and bonds [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 159.8 [1] 138.6 [1]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 159.8 [1] 138.6 [1]  
U.S. treasury notes and bonds [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 159.8 [1] 138.6 [1]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 159.8 [1] 138.6 [1]  
U.S. treasury notes and bonds [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 [1] 0 [1]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 [1] 0 [1]  
Mortgage-backed securities
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 50.3 55.8  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 50.3 55.8  
Mortgage-backed securities | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
Mortgage-backed securities | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 50.3 55.8  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 50.3 55.8  
Corporate fixed income and other securities [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 110.6 [2] 98.4 [2]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 110.6 [2] 98.4 [2]  
Corporate fixed income and other securities [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 [2] 0 [2]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 [2] 0 [2]  
Corporate fixed income and other securities [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 110.6 [2] 98.4 [2]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 110.6 [2] 98.4 [2]  
Mortgage-backed securities [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 22.3 [2] 13.5 [2]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 22.3 [2] 13.5 [2]  
Mortgage-backed securities [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 [2] 0 [2]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 [2] 0 [2]  
Mortgage-backed securities [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 22.3 [2] 13.5 [2]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 22.3 [2] 13.5 [2]  
Commingled fund [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 29.2 [3] 34.9 [3]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 29.2 [3] 34.9 [3]  
Commingled fund [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 [3] 0 [3]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 [3] 0 [3]  
Commingled fund [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 29.2 [3] 34.9 [3]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 29.2 [3] 34.9 [3]  
Common/collective trust [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 26.0 [4] 25.6 [4]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 26.0 [4] 25.6 [4]  
Common/collective trust [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 [4] 0 [4]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 [4] 0 [4]  
Common/collective trust [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 26.0 [4] 25.6 [4]  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 26.0 [4] 25.6 [4]  
Foreign government bonds [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 4.0 3.9  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 4.0 3.9  
Foreign government bonds [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
Foreign government bonds [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 4.0 3.9  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 4.0 3.9  
U.S. municipal bonds [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 2.0 0.8  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 2.0 0.8  
U.S. municipal bonds [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
U.S. municipal bonds [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 2.0 0.8  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 2.0 0.8  
Interest-bearing cash [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0.1 0.2  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0.1 0.2  
Interest-bearing cash [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0.1 0.2  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0.1 0.2  
Interest-bearing cash [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
Preferred stocks (foreign) [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets   0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending   0  
Preferred stocks (foreign) [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets   0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending   0  
Preferred stocks (foreign) [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets   0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending   0  
Receivable (foreign currency) [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 1.1 0.4  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 1.1 0.4  
Receivable (foreign currency) [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
Receivable (foreign currency) [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 1.1 0.4  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 1.1 0.4  
Payable (foreign currency) [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets (1.1) (0.4)  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending (1.1) (0.4)  
Payable (foreign currency) [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
Payable (foreign currency) [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets (1.1) (0.4)  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending (1.1) (0.4)  
Total Plan investments [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 680.4 643.8  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 680.4 643.8  
Total Plan investments [Member] | Fair Value, Inputs, Level 1 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 436.0 410.9  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 436.0 410.9  
Total Plan investments [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 244.4 232.9  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 244.4 232.9  
Receivable from broker for securities sold [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 11.5 0.8  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 11.5 0.8  
Interest and dividends receivable [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 3.2 2.8  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 3.2 2.8  
Payable to broker for securities purchased [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets (40.2) (21.4)  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending (40.2) (21.4)  
Total Plan assets [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 654.9 626.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 654.9 626.0  
Other Postretirement Benefit Plans, Defined Benefit [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 61.4 59.6  
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit Obligation, Ending (258.2) (301.0)  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Funded Status of Plan (196.8) (241.4)  
Fair Value of Plan Assets, Ending 61.4 59.6  
Pension Plan [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements 22.4 0 0
Fair Value of Plan Assets 654.9 626.0 589.8
Accumulated Benefit Obligation 623.4 705.2  
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit Obligation, Beginning (747.1) (697.7)  
Service cost (19.0) (17.9) 17.6
Actual return on plans' assets (26.7) (30.1) (33.3)
Plan amendments 0 0  
Plan settlements 67.5 0  
Participants' contributions 0 0  
Medicare subsidies received 0 0  
Actuarial gains (losses) 53.0 (61.4)  
Benefits paid (14.2) (60.0)  
Benefit Obligation, Ending (658.1) (747.1) (697.7)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Beginning 626.0 589.8  
Actual return on plans' assets 75.6 61.2  
Employer contributions 35.0 35.0  
Plan settlements (67.5) 0  
Participants' contributions 0 0  
Medicare subsidies received 0 0  
Benefits paid 14.2 60.0  
Funded Status of Plan (3.2) (121.1)  
Fair Value of Plan Assets, Ending 654.9 626.0 589.8
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]      
Service cost 19.0 17.9 (17.6)
Interest cost 26.7 30.1 33.3
Expected return on plan assets (48.4) (46.0) 45.5
Amortization of transition obligations 0 0 0
Amortization of net loss 26.5 23.8 19.2
Amortization of unrecognized prior service cost 1.8 2.2 2.4
Settlement 22.4 0 0
Net periodic benefit cost 48.0 28.0 27.0
Less: Amount paid by unconsolidated affiliates 5.9 0 0
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates 42.1 28.0 27.0
Capitalized Portion of Net Periodic Benefit Cost 5.7 6.5 6.1
Assumptions Used Calculating Benefit Obligation, Discount Rate 4.60% 3.70% 4.50%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets 8.00% 8.00% 8.00%
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase 4.20% 4.20% 4.40%
Pension Plan [Member] | OKLAHOMA
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements 17.0    
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]      
Settlement 17.0    
Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending 0 0  
Restoration of Retirement Income Plan [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements 0 0.9 0
Fair Value of Plan Assets 0 0 0
Accumulated Benefit Obligation 12.9 12.7  
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit Obligation, Beginning (14.5) (13.3)  
Service cost (1.2) (1.0) 1.0
Actual return on plans' assets (0.5) (0.6) (0.6)
Plan amendments 0 0  
Plan settlements 0 0  
Participants' contributions 0 0  
Medicare subsidies received 0 0  
Actuarial gains (losses) 2.0 (1.8)  
Benefits paid (0.2) (2.2)  
Benefit Obligation, Ending (14.0) (14.5) (13.3)
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 0.2 2.2  
Plan settlements 0 0  
Participants' contributions 0 0  
Medicare subsidies received 0 0  
Benefits paid 0.2 2.2  
Funded Status of Plan (14.0) (14.5)  
Fair Value of Plan Assets, Ending 0 0 0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]      
Service cost 1.2 1.0 (1.0)
Interest cost 0.5 0.6 0.6
Expected return on plan assets 0 0 0
Amortization of transition obligations 0 0 0
Amortization of net loss 0.4 0.4 0.4
Amortization of unrecognized prior service cost 0.3 0.7 0.7
Settlement 0 0.9 0
Net periodic benefit cost 2.4 3.6 2.7
Less: Amount paid by unconsolidated affiliates 0.1 0 0
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates 2.3 3.6 2.7
Pension Plan [Member]
     
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]      
Net periodic benefit cost 60.0 51.4 45.1
Pension Plan [Member] | OKLAHOMA
     
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]      
Additional Pension Expense to Meet State Requirements 5.8 8.3 10.8
Postretirement Benefit Plan [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements 0 0 0
Fair Value of Plan Assets 61.4 59.6 61.0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit Obligation, Beginning (301.0) (280.6)  
Service cost (4.3) (4.1) 3.5
Actual return on plans' assets (10.3) (11.9) (12.5)
Plan amendments 0 0  
Plan settlements 0 0  
Participants' contributions (3.4) (3.5)  
Medicare subsidies received 0 (0.5)  
Actuarial gains (losses) 46.7 (12.9)  
Benefits paid (14.1) (12.5)  
Benefit Obligation, Ending (258.2) (301.0) (280.6)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Beginning 59.6 61.0  
Actual return on plans' assets 3.7 4.5  
Employer contributions 8.8 2.6  
Plan settlements 0 0  
Participants' contributions 3.4 3.5  
Medicare subsidies received 0 0.5  
Benefits paid 14.1 12.5  
Funded Status of Plan (196.8) (241.4)  
Fair Value of Plan Assets, Ending 61.4 59.6 61.0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]      
Service cost 4.3 4.1 (3.5)
Interest cost 10.3 11.9 12.5
Expected return on plan assets (2.5) (3.0) 5.1
Amortization of transition obligations 0 2.7 2.7
Amortization of net loss 21.5 20.6 18.3
Amortization of unrecognized prior service cost (16.5) (16.5) (16.5)
Settlement 0 0 0
Net periodic benefit cost 17.1 19.8 15.4
Less: Amount paid by unconsolidated affiliates 1.5 0 0
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates 15.6 19.8 15.4
Capitalized Portion of Net Periodic Benefit Cost 3.5 5.5 3.8
Assumptions Used Calculating Benefit Obligation, Discount Rate 4.60% 3.60% 4.50%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets 4.00% 4.00% 6.50%
Health Care Cost Trend Rate Assumed for Next Fiscal Year 8.35% 8.55% 8.75%
Ultimate Health Care Cost Trend Rate 4.48% 4.48% 4.48%
Year that Rate Reaches Ultimate Trend Rate 2028 2028 2028
Postretirement Benefit Plan [Member] | OKLAHOMA
     
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]      
Additional Postretirement Medical Expense to Meet State Requirements 0.6 0.8 3.5
Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 2 [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair Value of Plan Assets 0 0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair Value of Plan Assets, Ending $ 0 $ 0  
Less Than 90% [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
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 Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
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 Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
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 Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
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 Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
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 Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
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 Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
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 Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target Plan Asset Allocations 50.00%    
Target Plan Asset Allocations Range Minimum 50.00%    
Target Plan Asset Allocations Range Maximum 60.00%    
Domestic Mid-Cap Equity [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target Plan Asset Allocations 15.00%    
Target Plan Asset Allocations Range Minimum 5.00%    
Target Plan Asset Allocations Range Maximum 25.00%    
Domestic Small-Cap Equity [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target Plan Asset Allocations 15.00%    
Target Plan Asset Allocations Range Minimum 5.00%    
Target Plan Asset Allocations Range Maximum 25.00%    
International Equity [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target Plan Asset Allocations 20.00%    
Target Plan Asset Allocations Range Minimum 10.00%    
Target Plan Asset Allocations Range Maximum 30.00%    
[1] This category represents U.S. treasury notes and bonds with a Moody's Investors Services rating of Aaa and Government Agency Bonds with a Moody's Investors Services rating of A1 or higher.
[2] This category primarily represents U.S. corporate bonds with an investment grade rating at or above Baa3 or BBB- by Moody's Investors Services, Standard & Poor's Ratings Services or Fitch Ratings.
[3] This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.
[4] This category represents units of participation in an investment pool which primarily invests in foreign or domestic bonds, debentures, mortgages, equipment or other trust certificates, notes, obligations issued or guaranteed by the U.S. Government or its agencies, bank certificates of deposit, bankers' acceptances and repurchase agreements, high grade commercial paper and other instruments with money market characteristics with a fixed or variable interest rate. There are no restrictions on redemptions in the common/collective trust.