Accounting Policies Accounting Policies (Revenue from Contracts with Customers) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended									12 Months Ended
		Dec. 29, 2017		Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 30, 2016	Sep. 30, 2016	Jul. 01, 2016	Apr. 01, 2016	Dec. 28, 2018	Dec. 29, 2017		Dec. 30, 2016		Jan. 01, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue		$ 785.5		$ 795.2	$ 785.5	$ 742.2	$ 699.8	$ 676.2	$ 659.9	$ 610.6	$ 3,108.4	$ 2,646.5	[1]	$ 2,362.1	[1]
Gross Profit		435.2		426.9	422.7	396.2	359.5	351.2	342.6	324.3	1,681.0	1,377.6	[1]	1,234.5	[1]
Operating Income (Loss)											320.7	235.7	[1]	180.4	[1]
Income tax provision (benefit)											(5.3)	129.7	[1]	43.9	[1]
Net income attributable to Trimble Inc.		$ 86.5		$ 73.7	$ 64.1	$ 58.5	$ (35.9)	$ 57.2	$ 47.3	$ 49.8	$ 282.8	$ 118.4	[1]	$ 132.4	[1]
Diluted earnings per share		$ 0.34		$ 0.29	$ 0.25	$ 0.23	$ (0.14)	$ 0.22	$ 0.18	$ 0.19	$ 1.12	$ 0.46	[1]	$ 0.52	[1]
Accounts receivable, net		$ 427.7	[2]				$ 366.2				$ 512.6	$ 427.7	[2]	$ 366.2
Inventories		264.6	[2]				213.3				298.0	264.6	[2]	213.3
Deferred costs, non-current		35.0	[2]								41.3	35.0	[2]
Other current and non-current assets		182.9										182.9
Current and non-current deferred revenue		276.6					246.4				387.2	276.6		246.4
Other current liabilities		99.2	[2]								118.5	99.2	[2]
Deferred income tax liabilities		47.8	[2]								73.8	47.8	[2]
Stockholders' Equity	[1]	2,414.5	[2]				$ 2,355.2				$ 2,674.8	2,414.5	[2]	2,355.2		$ 2,271.9
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												2,654.2		2,362.2
Gross Profit												1,392.6		1,238.0
Operating Income (Loss)												246.0		181.0
Income tax provision (benefit)												137.9		44.5
Net income attributable to Trimble Inc.												$ 121.1		$ 132.4
Diluted earnings per share												$ 0.47		$ 0.52
Accounts receivable, net		414.8										$ 414.8
Inventories		271.8										271.8
Deferred costs, non-current		0.0										0.0
Other current and non-current assets		205.5										205.5
Current and non-current deferred revenue		313.4										313.4
Other current liabilities		101.0										101.0
Deferred income tax liabilities		40.4										40.4
Stockholders' Equity		2,366.0										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												(7.7)		$ (0.1)
Gross Profit												(15.0)		(3.5)
Operating Income (Loss)												(10.3)		(0.6)
Income tax provision (benefit)												(8.2)		(0.6)
Net income attributable to Trimble Inc.												$ (2.7)		$ 0.0
Diluted earnings per share												$ (0.01)		$ 0.00
Accounts receivable, net		12.9										$ 12.9
Inventories		(7.2)										(7.2)
Deferred costs, non-current		35.0										35.0
Other current and non-current assets		(22.6)										(22.6)
Current and non-current deferred revenue		(36.8)										(36.8)
Other current liabilities		(1.8)										(1.8)
Deferred income tax liabilities		7.4										7.4
Stockholders' Equity		$ 48.5										$ 48.5

[1] See Note 2 for a summary of adjustments

[2] See Note 2 for a summary of adjustments