Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions		Sep. 28, 2018	Dec. 29, 2017
Loss Contingencies [Line Items]
Unconditional purchase obligations		$ 226.4
Business Combination, Contingent Consideration, Liability	[1]	$ 4.8	$ 14.2

[1] Contingent consideration liabilities represent arrangements to pay the former owners of certain companies that Trimble acquired. The undiscounted maximum payment under the arrangements is $52.6 million at the end of the third quarter of fiscal 2018. The fair values are estimated using scenario-based methods or option pricing methods based upon estimated future revenues, gross margins or other milestones. Contingent consideration liabilities are included in Other current liabilities and Other non-current liabilities on the Company's Condensed Consolidated Balance Sheets.