Updates to Significant Accounting Policies - Revenue From Contract With Customer (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			9 Months Ended
		Sep. 28, 2018	Sep. 29, 2017		Sep. 28, 2018	Sep. 29, 2017		Jun. 29, 2018	Dec. 29, 2017		Jun. 30, 2017	[5]	Dec. 30, 2016	[5]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		$ 795.2	$ 676.2	[1]	$ 2,322.9	$ 1,946.7	[1]
Gross margin		426.9	351.2	[1]	1,245.8	1,018.1	[1]
Consolidated operating income		77.4	66.3	[1],[2]	231.1	180.0	[1],[2]
Income tax provision (benefit)		(9.6)	14.7	[1]	13.5	45.3	[1]
Net income attributable to Trimble Inc.		$ 73.7	$ 57.2	[1]	$ 196.3	$ 154.3	[1]
Diluted earnings per share		$ 0.29	$ 0.22	[1]	$ 0.78	$ 0.60	[1]
Accounts receivable		$ 476.0			$ 476.0				$ 427.7	[3]
Inventories		286.3			286.3				264.6	[3],[4]
Deferred costs, non-current		37.2			37.2				35.0	[3]
Other current adn non-current assets									182.9
Current and non-current deferred revenue		364.3	$ 284.9	[5]	364.3	$ 284.9	[5]	$ 356.2	276.6		$ 307.3		$ 246.4
Other current liabilities		117.5			117.5				99.2	[3]
Deferred income tax liabilities		88.5			88.5				47.8	[3]
Total stockholders' equity		$ 2,648.6			$ 2,648.6				2,414.5	[3]
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue			670.0			1,945.8
Gross margin			349.5			1,022.6
Consolidated operating income			64.0			183.2
Income tax provision (benefit)			13.9			46.7
Net income attributable to Trimble Inc.			$ 55.7			$ 156.1
Diluted earnings per share			$ 0.22			$ 0.61
Accounts receivable									414.8
Inventories									271.8
Deferred costs, non-current									0.0
Other current adn non-current assets									205.5
Current and non-current deferred revenue									313.4
Other current liabilities									101.0
Deferred income tax liabilities									40.4
Total stockholders' equity									2,366.0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	[6]		$ 6.2			$ 0.9
Gross margin	[6]		1.7			(4.5)
Consolidated operating income	[6]		2.3			(3.2)
Income tax provision (benefit)	[6]		0.8			(1.4)
Net income attributable to Trimble Inc.	[6]		$ 1.5			$ (1.8)
Diluted earnings per share	[6]		$ 0.00			$ (0.01)
Accounts receivable	[6]								12.9
Inventories	[6]								(7.2)
Deferred costs, non-current	[6]								35.0
Other current adn non-current assets	[6]								(22.6)
Current and non-current deferred revenue	[6]								(36.8)
Other current liabilities	[6]								(1.8)
Deferred income tax liabilities	[6]								7.4
Total stockholders' equity	[6]								$ 48.5

[1] See Note 2 for a summary of adjustments

[2] See Note 2 for a summary of adjustments

[3] See Note 2 for a summary of adjustments

[4] See Note 2 for a summary of adjustments

[5] See Note 2 for a summary of adjustments

[6] Adjusted to reflect the adoption of Revenue from Contracts with Customers