Debt - Schedule of Long-term Debt (Details) - USD ($) $ in Millions		Oct. 31, 2017	Jan. 31, 2017	Oct. 31, 2016
Debt Instrument [Line Items]
Long-term Debt		$ 879.2	$ 878.4	$ 885.7
Long-term Debt, Gross		888.3	888.0	895.4
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net		9.1	9.6	9.7
2012 4.40% Series B Notes, due July 2042 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[1]	250.0	250.0	250.0
2014 3.80% Senior Notes, due October 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[2],[3]	250.0	250.0	250.0
2014 4.90% Senior Notes, due October 2044 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[2],[3]	300.0	300.0	300.0
2016 0.78% Senior Notes, due August 2026 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[2],[4]	$ 88.3	$ 88.0	$ 95.4

[1] a The agreements governing these Senior Notes require repayments of $50.0 million in aggregate every five years beginning in 2022.

[2] b These agreements require lump sum repayments upon maturity.

[3] c These Senior Notes were issued at a discount, which will be amortized until the debt maturity.

[4] d These Senior Notes were issued, at par, ¥10.0 billion.