Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended											12 Months Ended
	Jan. 31, 2016	[1]	Oct. 31, 2015	Jul. 31, 2015	[2]	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	[3]	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,213.6		$ 938.2	$ 990.5		$ 962.4	$ 1,285.3	$ 959.6		$ 992.9	$ 1,012.1	$ 4,104.9	$ 4,249.9	$ 4,031.1
Gross Profit	764.8		564.5	593.0		569.0	781.6	570.9		595.2	589.5	2,491.3	2,537.2	2,340.4
Earnings from operations	260.9		156.4	172.8		170.0	304.6	168.5		208.5	209.8	760.1	891.4	304.3
Net earnings	$ 163.2		$ 91.0	$ 104.9		$ 104.9	$ 196.2	$ 38.3		$ 124.1	$ 125.6	$ 463.9	$ 484.2	$ 181.4
Basic	$ 1.28		$ 0.71	$ 0.81		$ 0.81	$ 1.52	$ 0.30		$ 0.96	$ 0.97	$ 3.61	$ 3.75	$ 1.42
Diluted	$ 1.28		$ 0.70	$ 0.81		$ 0.81	$ 1.51	$ 0.29		$ 0.96	$ 0.97	$ 3.59	$ 3.73	$ 1.41

[1] On a pre-tax basis, includes charges for the quarter ended January 31, 2016 of: i.$28.3 million, which reduced net earnings per diluted share by $0.14, associated with an impairment charge related to a financing arrangement with Koidu Limited (see "Note B - Summary of Significant Accounting Policies" and "Note J - Commitments and Contingencies"); andii.$8.8 million, which reduced net earnings per diluted share by $0.04, associated with severance related to staffing reductions and subleasing of certain office space for which only a portion of the Company's future rent obligations will be recovered (see "Note J - Commitments and Contingencies").

[2] On a pre-tax basis, includes a charge of $9.6 million for the quarter ended July 31, 2015, which reduced net earnings per diluted share by $0.05, associated with an impairment charge related to a financing arrangement with Koidu Limited (see "Note B - Summary of Significant Accounting Policies" and "Note J - Commitments and Contingencies").

[3] On a pre-tax basis, includes a charge of $93.8 million for the quarter ended October 31, which reduced net earnings per diluted share by $0.47, associated with the redemption of $400.0 million in aggregate principal amount of the Private Placement Notes prior to their scheduled maturities (see "Note G - Debt").