Quarterly Financial Data (Unaudited) - (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,320.6	$ 1,012.4	$ 1,075.9	$ 1,033.2	$ 1,334.3	$ 976.2	$ 959.7	$ 899.6	$ 4,442.1	$ 4,169.8	$ 4,001.8
Gross profit	842.0	629.3	688.8	650.9	852.0	600.0	599.6	559.1	2,811.0	2,610.7	2,499.0
Earnings from operations	268.4	126.4	191.2	204.3	311.1	164.0	184.7	149.6	790.3	809.4	746.4
Net earnings	$ 204.5	$ 94.9	$ 144.7	$ 142.3	$ 61.9	$ 100.2	$ 115.0	$ 92.9	$ 586.4	$ 370.1	$ 446.1
Basic (usd per share)	$ 1.68	$ 0.78	$ 1.17	$ 1.14	$ 0.50	$ 0.81	$ 0.92	$ 0.75	$ 4.77	$ 2.97	$ 3.57
Diluted (usd per share)	$ 1.67	$ 0.77	$ 1.17	$ 1.14	$ 0.50	$ 0.80	$ 0.92	$ 0.74	$ 4.75	$ 2.96	$ 3.55