Quarterly Financial Data (Unaudited) - (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,357.8	$ 1,014.6	$ 1,048.5	$ 1,003.1	$ 1,320.6	$ 1,012.4	$ 1,075.9	$ 1,033.2	$ 4,424.0	$ 4,442.1	$ 4,169.8
Gross profit	859.3	625.7	657.7	619.2	842.0	629.3	688.8	650.9	2,761.9	2,811.0	2,610.7
Earnings from operations	268.9	118.5	184.3	160.9	268.4	126.4	191.2	204.3	732.6	790.3	809.4
Net earnings	$ 201.2	$ 78.4	$ 136.3	$ 125.2	$ 204.5	$ 94.9	$ 144.7	$ 142.3	$ 541.1	$ 586.4	$ 370.1
Basic (usd per share)	$ 1.67	$ 0.65	$ 1.13	$ 1.03	$ 1.68	$ 0.78	$ 1.17	$ 1.14	$ 4.47	$ 4.77	$ 2.97
Diluted (usd per share)	$ 1.66	$ 0.65	$ 1.12	$ 1.03	$ 1.67	$ 0.77	$ 1.17	$ 1.14	$ 4.45	$ 4.75	$ 2.96