XML 91 R69.htm IDEA: XBRL DOCUMENT v3.6.0.2
Retirement Plans and Postretirement Benefit Plans (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Pension Contributions     $ 20.0 $ 0.0  
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, Net Periodic Benefit Cost [Abstract]          
Net periodic benefit cost     $ 22.5 40.2 $ 19.3
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     0.2 0.2 0.1
Effect of One Percentage Point Decrease on Service and Interest Cost Components     0.0 0.1 0.1
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation     0.7 0.7 0.7
Expected Future Benefit Payments, Next Twelve Months     48.7    
Expected Future Benefit Payments, Year Two     48.7    
Expected Future Benefit Payments, Year Three     51.9    
Expected Future Benefit Payments, Year Four     54.6    
Expected Future Benefit Payments, Year Five     55.7    
Expected Future Benefit Payments, Five Fiscal Years Thereafter     290.1    
Defined Contribution Plan, Cost Recognized     11.9 11.6 15.2
Pension Plans, Defined Benefit [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Accumulated Benefit Obligation $ 610.9   608.0 610.9  
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]          
Benefit Obligation, Beginning     680.0 725.0  
Service cost     15.8 16.1 15.3
Interest cost     25.5 26.1 28.1
Plan settlements     0.0 (60.7)  
Participants' contributions     0.0 0.0  
Actuarial gains (losses)     4.7 (11.3)  
Benefits paid     (53.8) (15.2)  
Benefit Obligation, Ending 680.0   672.2 680.0 725.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     581.7 679.8  
Actual return on plans' assets     48.0 (22.2)  
Employer contributions     20.0 0.0  
Plan settlements     0.0 (60.7)  
Participants' contributions     0.0 0.0  
Benefits paid     (53.8) (15.2)  
Fair Value of Plan Assets, Ending 581.7   595.9 581.7 679.8
Funded Status of Plan (98.3)   (76.3) (98.3)  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Service cost     15.8 16.1 15.3
Interest cost     25.5 26.1 28.1
Expected return on plan assets     (41.5) (46.0) (45.3)
Amortization of net loss     16.5 18.0 14.3
Amortization of unrecognized prior service cost [1]     (0.1) 0.4 1.7
Curtailment     0.0 0.0 (0.2)
Settlement $ 5.5 $ 16.2 0.0 21.7 0.0
Net periodic benefit cost     16.2 36.3 13.9
Amount paid by unconsolidated affiliates     5.1 4.2 3.2
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates [2]     11.1 32.1 10.7
Plan settlements     0.0 (60.7)  
Capitalized Portion of Net Periodic Benefit Cost     $ 4.0 $ 5.0 $ 3.4
Assumptions Used Calculating Benefit Obligation, Discount Rate 4.00%   4.00% 4.00% 3.80%
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     $ 581.7 $ 679.8  
Pension Plans, Defined Benefit [Member] | OKLAHOMA          
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Additional Pension Expense to Meet State Requirements     9.9 (3.1) $ 11.2
Pension Plans, Defined Benefit [Member] | ARKANSAS          
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]          
Plan settlements     0.1 1.9  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Plan settlements     0.1 1.9  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Plan settlements     0.1 1.9  
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 [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | U.S. common stocks [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     208.2    
Fair Value of Plan Assets, Ending 208.2   237.1 208.2  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     208.2    
Pension Plans, Defined Benefit [Member] | U.S. common stocks [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     208.2    
Fair Value of Plan Assets, Ending 208.2   237.1 208.2  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     208.2    
Pension Plans, Defined Benefit [Member] | U.S. common stocks [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | U.S. treasury notes and bonds [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure [3] 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning [3]     158.9    
Fair Value of Plan Assets, Ending [3] 158.9   122.3 158.9  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning [3]     158.9    
Pension Plans, Defined Benefit [Member] | U.S. treasury notes and bonds [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 [3]     158.9    
Fair Value of Plan Assets, Ending [3] 158.9   122.3 158.9  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning [3]     158.9    
Pension Plans, Defined Benefit [Member] | U.S. treasury notes and bonds [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 [3]     0.0    
Fair Value of Plan Assets, Ending [3] 0.0   0.0 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning [3]     0.0    
Pension Plans, Defined Benefit [Member] | Mortgage-backed securities          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     14.5    
Fair Value of Plan Assets, Ending 14.5   59.2 14.5  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     14.5    
Pension Plans, Defined Benefit [Member] | Mortgage-backed securities | 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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Mortgage-backed securities | Fair Value, Inputs, Level 2 [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     14.5    
Fair Value of Plan Assets, Ending 14.5   59.2 14.5  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     14.5    
Pension Plans, Defined Benefit [Member] | Corporate fixed income and other securities [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     140.2    
Fair Value of Plan Assets, Ending 140.2   137.6 140.2  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     140.2    
Pension Plans, Defined Benefit [Member] | Corporate fixed income and other securities [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Corporate fixed income and other securities [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     140.2    
Fair Value of Plan Assets, Ending 140.2   137.6 140.2  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     140.2    
Pension Plans, Defined Benefit [Member] | Commingled fund [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure [4] 24.4   23.8 24.4  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning [4]     24.4    
Fair Value of Plan Assets, Ending [4] 24.4   23.8 24.4  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning [4]     24.4    
Pension Plans, Defined Benefit [Member] | Commingled fund [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 [4]     0.0    
Fair Value of Plan Assets, Ending [4] 0.0   0.0 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning [4]     0.0    
Pension Plans, Defined Benefit [Member] | Commingled fund [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]     0.0    
Fair Value of Plan Assets, Ending [4] 0.0   0.0 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning [4]     0.0    
Pension Plans, Defined Benefit [Member] | Foreign government bonds [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     5.6    
Fair Value of Plan Assets, Ending 5.6   5.2 5.6  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     5.6    
Pension Plans, Defined Benefit [Member] | Foreign government bonds [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Foreign government bonds [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     5.6    
Fair Value of Plan Assets, Ending 5.6   5.2 5.6  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     5.6    
Pension Plans, Defined Benefit [Member] | Interest-bearing cash [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0     0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     0.4    
Fair Value of Plan Assets, Ending 0.4     0.4  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.4    
Pension Plans, Defined Benefit [Member] | Interest-bearing cash [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     0.4    
Fair Value of Plan Assets, Ending 0.4     0.4  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.4    
Pension Plans, Defined Benefit [Member] | Interest-bearing cash [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 [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Municipal bonds [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     4.9    
Fair Value of Plan Assets, Ending 4.9   1.9 4.9  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     4.9    
Pension Plans, Defined Benefit [Member] | Municipal bonds [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Municipal bonds [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     4.9    
Fair Value of Plan Assets, Ending 4.9   1.9 4.9  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     4.9    
Pension Plans, Defined Benefit [Member] | Money market funds [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 11.7   2.2 11.7  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     11.7    
Fair Value of Plan Assets, Ending 11.7   2.2 11.7  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     11.7    
Pension Plans, Defined Benefit [Member] | Money market funds [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Money market funds [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Mutual fund [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     24.3    
Fair Value of Plan Assets, Ending 24.3   9.0 24.3  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     24.3    
Pension Plans, Defined Benefit [Member] | Mutual fund [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     24.3    
Fair Value of Plan Assets, Ending 24.3   9.0 24.3  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     24.3    
Pension Plans, Defined Benefit [Member] | Mutual fund [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Treasury futures, receivable [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     17.6    
Fair Value of Plan Assets, Ending 17.6   10.7 17.6  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     17.6    
Pension Plans, Defined Benefit [Member] | Treasury futures, receivable [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Treasury futures, receivable [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     17.6    
Fair Value of Plan Assets, Ending 17.6   10.7 17.6  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     17.6    
Pension Plans, Defined Benefit [Member] | Treasury futures, payable [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     (12.4)    
Fair Value of Plan Assets, Ending (12.4)   (2.3) (12.4)  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     (12.4)    
Pension Plans, Defined Benefit [Member] | Treasury futures, payable [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Treasury futures, payable [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     (12.4)    
Fair Value of Plan Assets, Ending (12.4)   (2.3) (12.4)  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     (12.4)    
Pension Plans, Defined Benefit [Member] | Cash collateral [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure     0.0    
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Ending     0.3    
Pension Plans, Defined Benefit [Member] | Cash collateral [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     0.3    
Pension Plans, Defined Benefit [Member] | Cash collateral [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    
Pension Plans, Defined Benefit [Member] | Receivable (foreign currency) [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0   0.0 0.0  
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   0.2 0.1  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.1    
Pension Plans, Defined Benefit [Member] | Receivable (foreign currency) [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Receivable (foreign currency) [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   0.2 0.1  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.1    
Pension Plans, Defined Benefit [Member] | Payable (foreign currency) [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0     0.0  
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 [Abstract]          
Fair Value of Plan Assets, Beginning     (0.1)    
Pension Plans, Defined Benefit [Member] | Payable (foreign currency) [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 [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Payable (foreign currency) [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 [Abstract]          
Fair Value of Plan Assets, Beginning     (0.1)    
Pension Plans, Defined Benefit [Member] | Index fund [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0     0.0  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     1.8    
Fair Value of Plan Assets, Ending 1.8     1.8  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     1.8    
Pension Plans, Defined Benefit [Member] | Index fund [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     1.8    
Fair Value of Plan Assets, Ending 1.8     1.8  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     1.8    
Pension Plans, Defined Benefit [Member] | Index fund [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 [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Preferred stocks (foreign) [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 0.0     0.0  
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 0.3     0.3  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.3    
Pension Plans, Defined Benefit [Member] | Preferred stocks (foreign) [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     0.3    
Fair Value of Plan Assets, Ending 0.3     0.3  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.3    
Pension Plans, Defined Benefit [Member] | Preferred stocks (foreign) [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 [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Total Plan investments [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Alternative Investments, Fair Value Disclosure 36.1   26.0 36.1  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     600.4    
Fair Value of Plan Assets, Ending 600.4   607.2 600.4  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     600.4    
Pension Plans, Defined Benefit [Member] | Total Plan investments [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     393.9    
Fair Value of Plan Assets, Ending 393.9   368.7 393.9  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     393.9    
Pension Plans, Defined Benefit [Member] | Total Plan investments [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     170.4    
Fair Value of Plan Assets, Ending 170.4   212.5 170.4  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     170.4    
Pension Plans, Defined Benefit [Member] | Receivable from broker for securities sold [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 0.0  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     0.0    
Pension Plans, Defined Benefit [Member] | Interest and dividends receivable [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     3.5    
Fair Value of Plan Assets, Ending 3.5   3.0 3.5  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     3.5    
Pension Plans, Defined Benefit [Member] | Payable to broker for securities purchased [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     (22.2)    
Fair Value of Plan Assets, Ending (22.2)   (14.3) (22.2)  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     (22.2)    
Pension Plans, Defined Benefit [Member] | Total Plan assets [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair Value of Plan Assets, Beginning     581.7    
Fair Value of Plan Assets, Ending 581.7   595.9 581.7  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Fair Value of Plan Assets, Beginning     581.7    
Restoration of Retirement Income Plan [Member]          
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]          
Accumulated Benefit Obligation 24.6   6.1 24.6  
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]          
Benefit Obligation, Beginning     25.1 19.7  
Service cost     0.3 1.3 1.1
Interest cost     0.4 0.7 0.6
Plan settlements     (20.6) 0.0  
Participants' contributions     0.0 0.0  
Actuarial gains (losses)     1.8 4.0  
Benefits paid     0.0 (0.6)  
Benefit Obligation, Ending 25.1   7.0 25.1 19.7
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     20.6 0.6  
Plan settlements     (20.6) 0.0  
Participants' contributions     0.0 0.0  
Benefits paid     0.0 (0.6)  
Fair Value of Plan Assets, Ending 0.0   0.0 0.0 0.0
Funded Status of Plan $ (25.1)   (7.0) (25.1)  
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Service cost     0.3 1.3 1.1
Interest cost     0.4 0.7 0.6
Expected return on plan assets     0.0 0.0 0.0
Amortization of net loss     0.7 0.6 0.2
Amortization of unrecognized prior service cost [1]     0.1 0.1 0.2
Curtailment     0.0 0.0 0.0
Settlement     8.6 0.0 0.0
Net periodic benefit cost     10.1 2.7 2.1
Amount paid by unconsolidated affiliates     0.3 0.1 0.1
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates [2]     9.8 2.6 $ 2.0
Plan settlements     (20.6) 0.0  
Fair Value of Plan Assets, Beginning     $ 0.0 $ 0.0  
Less Than 90% [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost [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 [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 [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 [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 [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 [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 [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 [Abstract]          
Target Plan Asset Allocations     40.00%    
Target Plan Asset Allocations Range Minimum     35.00%    
Target Plan Asset Allocations Range Maximum     60.00%    
Domestic Mid-Cap Equity [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
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 Plan, Net Periodic Benefit Cost [Abstract]          
Target Plan Asset Allocations     25.00%    
Target Plan Asset Allocations Range Minimum     5.00%    
Target Plan Asset Allocations Range Maximum     30.00%    
International Equity [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]          
Target Plan Asset Allocations     20.00%    
Target Plan Asset Allocations Range Minimum     10.00%    
Target Plan Asset Allocations Range Maximum     30.00%    
[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] In addition to the $22.5 million, $40.2 million and $19.3 million of net periodic benefit cost recognized in 2016, 2015 and 2014, respectively, OG&E recognized the following: •a change in pension expense in 2016, 2015 and 2014 of $9.9 million, $(3.1) million and $11.2 million, respectively, to maintain the allowable amount to be recovered for pension expense in the Oklahoma jurisdiction, which are included in the Pension tracker regulatory asset or liability (see Note 1); •an increase in postretirement medical expense in 2016, 2015 and 2014 of $7.9 million, $5.8 million and $5.2 million, respectively, to maintain the allowable amount to be recovered for postretirement medical expense in the Oklahoma jurisdiction which are included in the Pension tracker regulatory asset or liability (see Note 1); and •a deferral of pension expense in 2016 and 2015 of $0.1 million and $1.9 million related to the Arkansas jurisdictional portion of the pension settlement charge of $8.6 million and $21.7 million, respectively.
[3] 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.
[4] This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.