Employee Benefit Plans - Projected Benefit Obligation, Plan Assets and Accumulated Benefit Obligation (Details) - USD ($) $ in Millions	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 668.7	$ 549.7
Qualified
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	800.3	658.5
Fair value of plan assets	668.7	549.7
Funded status at end of year	(131.6)	(108.8)
Accumulated benefit obligation	722.1	598.8
Excess/SRIP
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	127.8	109.4
Fair value of plan assets	0.0	0.0
Funded status at end of year	(127.8)	(109.4)
Accumulated benefit obligation	110.6	94.0
Other
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	28.0	27.1
Fair value of plan assets	0.0	0.0
Funded status at end of year	(28.0)	(27.1)
Accumulated benefit obligation	22.8	22.2
Total
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	956.1	795.0	$ 795.6
Fair value of plan assets	668.7	549.7	$ 578.1
Funded status at end of year	(287.4)	(245.3)
Accumulated benefit obligation	$ 855.5	$ 715.0