Debt Senior Notes (Details) ¥ in Millions, $ in Millions	12 Months Ended
	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)	Jan. 31, 2016 USD ($)	Jan. 31, 2018 JPY (¥)	Jan. 31, 2018 USD ($)
Debt Instrument [Line Items]
Proceeds from issuance of long-term debt	$ 0.0	$ 98.1	$ 0.0
2012 4.40% Series B Notes, due July 2042 [Member]
Debt Instrument [Line Items]
Debt Instrument, Periodic Payment, Principal	$ 50.0
Debt Instrument, Face Amount					$ 250.0
Debt Instrument, Interest Rate, Stated Percentage				4.40%	4.40%
2014 3.80% Senior Notes, due October 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				3.80%	3.80%
2014 4.90% Senior Notes, due October 2044 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				4.90%	4.90%
2016 0.78% Senior Notes, due August 2026 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount				¥ 10,000.0	$ 91.9
Debt Instrument, Interest Rate, Stated Percentage				0.78%	0.78%
2010 1.72% Notes, due September 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount | ¥				¥ 10,000.0
Debt Instrument, Interest Rate, Stated Percentage				1.72%	1.72%