Segments - Operations by geographic area (Details) - USD ($) $ in Millions		3 Months Ended									12 Months Ended
		Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	[1]	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Segment Reporting Information [Line Items]
Net revenue		$ 478.8	$ 489.6	$ 550.7		$ 511.9	$ 648.3	$ 599.8	$ 609.5	$ 646.5	$ 2,031.0	$ 2,504.1	$ 2,512.2
Total long-lived assets	[2]	158.6					169.3				158.6	169.3
Operating Segments
Segment Reporting Information [Line Items]
Net revenue											2,031.0	2,504.1	2,512.2
Architecture, Engineering, and Construction | Operating Segments
Segment Reporting Information [Line Items]
Net revenue											880.9	949.1	872.6
Manufacturing | Operating Segments
Segment Reporting Information [Line Items]
Net revenue											625.8	724.6	675.6
AutoCAD and AutoCAD LT | Operating Segments
Segment Reporting Information [Line Items]
Net revenue											326.7	594.8	695.1
Media and Entertainment | Operating Segments
Segment Reporting Information [Line Items]
Net revenue											138.9	160.0	167.3
Other | Operating Segments
Segment Reporting Information [Line Items]
Net revenue											58.7	75.6	101.6
Americas
Segment Reporting Information [Line Items]
Net revenue											871.9	972.8	898.0
Total long-lived assets	[2]	124.7					122.0				124.7	122.0
Europe, Middle East, and Africa
Segment Reporting Information [Line Items]
Net revenue											800.4	934.6	980.0
Asia Pacific
Segment Reporting Information [Line Items]
Net revenue											358.7	596.7	634.2
Total long-lived assets	[2]	15.2					21.6				15.2	21.6
U.S. | Americas
Segment Reporting Information [Line Items]
Net revenue											742.1	803.9	736.4
Total long-lived assets	[2]	118.8					118.8				118.8	118.8
Other Americas | Americas
Segment Reporting Information [Line Items]
Net revenue											129.8	168.9	$ 161.6
Total long-lived assets	[2]	5.9					3.2				5.9	3.2
Europe, Middle East, and Africa | Europe, Middle East, and Africa
Segment Reporting Information [Line Items]
Total long-lived assets	[2]	$ 18.7					$ 25.7				$ 18.7	$ 25.7

[1] Certain first quarter fiscal 2017 balances have been revised to reflect the adoption of ASU 2016-09. As the adoption occurred in the second quarter of fiscal 2017, we are required to reflect any adjustments as of February 1, 2016, the beginning of the annual period that includes the interim period of adoption, and are required to revise our reported quarterly results for the first quarter. The revision resulted in a $5.3 million decrease of stock-based compensation expense from the previously reported expense. See Note 1, "Business and Summary of Significant Accounting Policies" for further discussion on the adoption.

[2] (1)Long-lived assets exclude deferred tax assets, marketable securities, goodwill, and other intangible assets.