Non-controlling interests (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017
Noncontrolling Interest Items [Abstract]
Balance	[1]			$ 1,279.1
Net income		$ 42.9	$ 42.9	129.2	$ 122.3
Other comprehensive income (loss)		(18.9)	$ 9.1	(54.1)	$ 37.3
Dividends declared				(5.3)
Dividends to non-controlling interests				(1.6)
Capital contribution from non-controlling interests				3.7
Issuance of shares pursuant to employee stock compensation plans				2.2
Stock based compensation				4.7
Purchase of common stock				(16.4)
Balance	[2]	1,341.6		1,341.6
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
Capital contribution from 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
Capital contribution from non-controlling interests				0.0
Issuance of shares pursuant to employee stock compensation plans				2.2
Stock based compensation				4.7
Purchase of common stock				0.0
Balance		429.6		429.6
Retained Earnings [Member]
Noncontrolling Interest Items [Abstract]
Balance				1,607.2
Net income				125.9
Other comprehensive income (loss)				0.0
Dividends declared				(5.3)
Dividends to non-controlling interests				0.0
Capital contribution from 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		1,727.9		1,727.9
Accumulated Other Comprehensive Income (Loss) [Member]
Noncontrolling Interest Items [Abstract]
Balance				(186.1)
Net income				0.0
Other comprehensive income (loss)				(52.7)
Dividends declared				0.0
Dividends to non-controlling interests				0.0
Capital contribution from 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		(238.8)		(238.8)
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
Capital contribution from 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				(16.4)
Balance		(613.4)		(613.4)
Non-controlling Interests [Member]
Noncontrolling Interest Items [Abstract]
Balance				27.4
Net income				3.3
Other comprehensive income (loss)				(1.4)
Dividends declared				0.0
Dividends to non-controlling interests				(1.6)
Capital contribution from non-controlling interests				3.7
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Purchase of common stock				0.0
Balance		$ 31.4		$ 31.4

[1] Condensed from audited financial statements

[2] Unaudited