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, 2020	Jan. 31, 2019	Jan. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 17.0	$ 17.9	$ 17.3
Interest cost	32.5	30.7	32.0
Expected return on plan assets	(36.7)	(33.4)	(32.9)
Amortization of prior service cost (credit)	0.1	0.1	0.2
Amortization of net loss (gain)	11.3	15.0	13.2
Net periodic benefit cost	24.2	30.3	29.8
Net actuarial loss (gain)	66.6	31.2	(32.1)
Recognized actuarial (loss) gain	(11.3)	(15.0)	(13.2)
Recognized prior service (cost) credit	(0.1)	(0.1)	(0.2)
Total recognized in other comprehensive earnings	55.2	16.1	(45.5)
Total recognized in net periodic benefit cost and other comprehensive earnings	79.4	46.4	(15.7)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.6	3.0	2.8
Interest cost	3.3	3.0	3.0
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service cost (credit)	(0.6)	(0.7)	(0.7)
Amortization of net loss (gain)	(0.1)	0.1	0.1
Net periodic benefit cost	5.2	5.4	5.2
Net actuarial loss (gain)	15.4	(7.0)	1.5
Recognized actuarial (loss) gain	0.1	(0.1)	(0.1)
Recognized prior service (cost) credit	0.6	0.7	0.7
Total recognized in other comprehensive earnings	16.1	(6.4)	2.1
Total recognized in net periodic benefit cost and other comprehensive earnings	$ 21.3	$ (1.0)	$ 7.3