Employee Benefit Plans - Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Earnings (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 24.2	$ (30.6)	$ (14.1)
Recognized actuarial loss	(15.1)	(13.3)	(14.7)
Recognized prior service (cost) credit	0.6	0.5	0.7
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	17.9	17.3	17.4
Interest cost	30.7	32.0	31.6
Expected return on plan assets	(33.4)	(32.9)	(23.5)
Amortization of prior service cost	0.1	0.2	0.0
Amortization of net loss	15.0	13.2	14.7
Net periodic benefit cost	30.3	29.8	40.2
Net actuarial loss (gain)	31.2	(32.1)	(3.6)
Recognized actuarial loss	(15.0)	(13.2)	(14.7)
Recognized prior service (cost) credit	(0.1)	(0.2)	0.0
Total recognized in other comprehensive earnings	16.1	(45.5)	(18.3)
Total recognized in net periodic benefit cost and other comprehensive earnings	46.4	(15.7)	21.9
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	3.0	2.8	2.8
Interest cost	3.0	3.0	3.1
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service cost	(0.7)	(0.7)	(0.7)
Amortization of net loss	0.1	0.1	0.0
Net periodic benefit cost	5.4	5.2	5.2
Net actuarial loss (gain)	(7.0)	1.5	(10.5)
Recognized actuarial loss	(0.1)	(0.1)	0.0
Recognized prior service (cost) credit	0.7	0.7	0.7
Total recognized in other comprehensive earnings	(6.4)	2.1	(9.8)
Total recognized in net periodic benefit cost and other comprehensive earnings	$ (1.0)	$ 7.3	$ (4.6)