Retirement Benefit Plans - Benefit Cost Assumptions (Details)	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Retirement Benefits [Abstract]
Discount rate	2.40%	3.20%	3.20%
Expected long-term rate of return on plan assets	3.30%	4.30%	3.80%
Rate of compensation increase	2.30%	2.20%	2.20%