Non-controlling interests (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Noncontrolling Interest Items [Abstract]
Balance	[1]			$ 1,279.1
Net income		$ 45.2	$ 43.8	86.3	$ 79.4
Other comprehensive income (loss)		(53.9)	$ 14.0	(35.1)	$ 28.3
Dividends declared				(3.5)
Dividends to non-controlling interests				(0.2)
Issuance of shares pursuant to employee stock compensation plans				1.9
Stock based compensation				2.3
Purchase of common stock				(13.3)
Balance	[2]	1,317.4		1,317.4
Common Stock [Member]
Noncontrolling Interest Items [Abstract]
Balance				4.9
Net income				0.0
Other comprehensive income (loss)				0.0
Dividends declared				0.0
Dividends to non-controlling interests				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Purchase of common stock				0.0
Balance		4.9		4.9
Additional Paid-in Capital [Member]
Noncontrolling Interest Items [Abstract]
Balance				422.7
Net income				0.0
Other comprehensive income (loss)				0.0
Dividends declared				0.0
Dividends to non-controlling interests				0.0
Issuance of shares pursuant to employee stock compensation plans				1.9
Stock based compensation				2.3
Purchase of common stock				0.0
Balance		426.9		426.9
Retained Earnings [Member]
Noncontrolling Interest Items [Abstract]
Balance				1,607.2
Net income				84.0
Other comprehensive income (loss)				0.0
Dividends declared				(3.5)
Dividends to non-controlling interests				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Purchase of common stock				0.0
Balance		1,687.7		1,687.7
Accumulated Other Comprehensive Income (Loss) [Member]
Noncontrolling Interest Items [Abstract]
Balance				(186.1)
Net income				0.0
Other comprehensive income (loss)				(34.1)
Dividends declared				0.0
Dividends to non-controlling interests				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Purchase of common stock				0.0
Balance		(220.2)		(220.2)
Treasury Stock [Member]
Noncontrolling Interest Items [Abstract]
Balance				(597.0)
Net income				0.0
Other comprehensive income (loss)				0.0
Dividends declared				0.0
Dividends to non-controlling interests				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Purchase of common stock				(13.3)
Balance		(610.4)		(610.4)
Non-controlling Interests [Member]
Noncontrolling Interest Items [Abstract]
Balance				27.4
Net income				2.3
Other comprehensive income (loss)				(1.0)
Dividends declared				0.0
Dividends to non-controlling interests				(0.2)
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Purchase of common stock				0.0
Balance		$ 28.5		$ 28.5

[1] Condensed from audited financial statements

[2] Unaudited