Debt Long-term Debt Table (Details) $ in Millions, ¥ in Billions		3 Months Ended
		Apr. 30, 2016 USD ($)	Apr. 30, 2016 JPY (¥)	Apr. 30, 2016 USD ($)	Jan. 31, 2016 USD ($)	Apr. 30, 2015 USD ($)
Debt Instrument [Line Items]
Unsecured Senior Notes				$ 892.5	$ 884.2	$ 884.0
Current portion of long-term debt				92.5	84.2	0.0
Unamortized discounts and debt issuance costs				9.8	10.0	10.4
Long-term debt				790.2	790.0	873.6
2010 1.72% Notes, due September 2016 [Member]
Debt Instrument [Line Items]
Unsecured Senior Notes	[1],[2]			92.5	84.2	84.0
Debt Instrument, Face Amount | ¥			¥ 10.0
2012 4.40% Series B Notes, due July 2042 [Member]
Debt Instrument [Line Items]
Unsecured Senior Notes	[3]			250.0	250.0	250.0
Debt Instrument, Periodic Payment, Principal		$ 50.0
2014 3.80% Senior Notes, due October 2024 [Member]
Debt Instrument [Line Items]
Unsecured Senior Notes	[2],[4]			250.0	250.0	250.0
2014 4.90% Senior Notes, due October 2044 [Member]
Debt Instrument [Line Items]
Unsecured Senior Notes	[2],[4]			$ 300.0	$ 300.0	$ 300.0

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

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

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

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