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Employee Benefit Plans - Pension and Other Postretirement Benefits (Details)
$ in Millions
1 Months Ended 12 Months Ended
Mar. 22, 2019
USD ($)
Jan. 31, 2019
USD ($)
year
Jan. 31, 2018
USD ($)
Jan. 31, 2017
USD ($)
Defined Benefit Plan Disclosure [Line Items]        
Liability, defined benefit plan, current   $ 9.0 $ 8.6  
Pension/postretirement benefit obligations   $ 312.4 287.4  
Health care cost trend rate, assumed for next year (percentage)   6.75%    
Health care cost trend rate (percentage)   4.75%    
Qualified        
Defined Benefit Plan Disclosure [Line Items]        
Years used to calculate average compensation (years) | year   5    
Service period (years)   10 years    
Employer contribution   $ 11.8 $ 15.0 $ 120.0
Qualified | Equity Securities, Investment Summary        
Defined Benefit Plan Disclosure [Line Items]        
Defined benefit plan assets, target allocation (percentage)   50.00%    
Qualified | Fixed Income Securities        
Defined Benefit Plan Disclosure [Line Items]        
Defined benefit plan assets, target allocation (percentage)   35.00%    
Qualified | Other Investments        
Defined Benefit Plan Disclosure [Line Items]        
Defined benefit plan assets, target allocation (percentage)   15.00%    
Excess/SRIP        
Defined Benefit Plan Disclosure [Line Items]        
Service period (years)   10 years    
Subsequent Event | Qualified        
Defined Benefit Plan Disclosure [Line Items]        
Employer contribution $ 30.0