Segment Information Revenue from External Customers by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	Jan. 31, 2018	[1]	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	[2]	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Revenue from External Customer [Line Items]
Net sales	$ 1,334.3		$ 976.2	$ 959.7	$ 899.6	$ 1,229.6		$ 949.3	$ 931.6	$ 891.3	$ 4,169.8	$ 4,001.8	$ 4,104.9
Jewelry collections [Member]
Revenue from External Customer [Line Items]
Net sales											2,193.2	2,043.9	2,129.2
Engagement jewelry [Member]
Revenue from External Customer [Line Items]
Net sales											1,065.4	1,122.0	1,142.2
Designer jewelry [Member]
Revenue from External Customer [Line Items]
Net sales											551.2	529.1	526.4
Other products/services [Member]
Revenue from External Customer [Line Items]
Net sales											$ 360.0	$ 306.8	$ 307.1

[1] For the quarter ended January 31, 2018, includes net tax expense of $146.2 million, or $1.17 per diluted share, related to the estimated impact of the 2017 Tax Act (see "Note O. Income Taxes").

[2] On a pre-tax basis, includes charges for the quarter ended January 31, 2017 of: i.$25.4 million, which reduced net earnings per diluted share by $0.13, associated with an impairment charge related to software costs capitalized in connection with the development of a new finished goods inventory management and merchandising information system (see "Note B. Summary of Significant Accounting Policies" and "Note E. Property, Plant and Equipment"); andii.$12.6 million, which reduced net earnings per diluted share by $0.06, associated with impairment charges related to financing arrangements with diamond mining and exploration companies (see "Note B. Summary of Significant Accounting Policies").