Debt Long Term Debt Table (Details) ¥ in Millions, $ in Millions		Jan. 31, 2018 JPY (¥)	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)
Debt Instrument [Line Items]
Long-term debt, including current maturities			$ 891.9	$ 888.0
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net			9.0	9.6
Long-term debt			$ 882.9	878.4
2010 1.72% Notes, due September 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		1.72%	1.72%
Debt Instrument, Face Amount | ¥		¥ 10,000.0
2012 4.40% Series B Notes, due July 2042 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.40%	4.40%
Debt Instrument, Face Amount			$ 250.0
Long-term debt, including current maturities	[1]		$ 250.0	250.0
2014 3.80% Senior Notes, due October 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.80%	3.80%
Long-term debt, including current maturities	[2],[3]		$ 250.0	250.0
2014 4.90% Senior Notes, due October 2044 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.90%	4.90%
Long-term debt, including current maturities	[2],[3]		$ 300.0	300.0
2016 0.78% Senior Notes, due August 2026 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		0.78%	0.78%
Debt Instrument, Face Amount		¥ 10,000.0	$ 91.9
Long-term debt, including current maturities	[3],[4]		$ 91.9	$ 88.0

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

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

[3] These agreements require lump sum repayments upon maturity.

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