Non-controlling interests (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jul. 02, 2017	Jul. 03, 2016	Jul. 02, 2017	Jul. 03, 2016
Noncontrolling Interest [Line Items]
Balance	[1]			$ 1,030.9
Net income		$ 43.8	$ 22.3	79.4	$ 57.1
Other comprehensive income (loss)		14.0	$ (8.5)	28.3	$ 2.6
Dividends declared				(3.5)
Dividends to non-controlling interest				(1.7)
Issuance of shares pursuant to employee stock compensation plans				2.5
Stock based compensation				3.0
Balance	[2]	1,139.0		1,139.0
Common Stock [Member]
Noncontrolling Interest [Line Items]
Balance				4.8
Net income				0.0
Other comprehensive income (loss)				0.0
Dividends declared				0.0
Dividends to non-controlling interest				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Balance		4.8		4.8
Additional Paid-in Capital [Member]
Noncontrolling Interest [Line Items]
Balance				400.0
Net income				0.0
Other comprehensive income (loss)				0.0
Dividends declared				0.0
Dividends to non-controlling interest				0.0
Issuance of shares pursuant to employee stock compensation plans				2.5
Stock based compensation				3.0
Balance		405.5		405.5
Retained Earnings [Member]
Noncontrolling Interest [Line Items]
Balance				1,419.1
Net income				77.6
Other comprehensive income (loss)				0.0
Dividends declared				(3.5)
Dividends to non-controlling interest				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Balance		1,493.3		1,493.3
Accumulated Other Comprehensive Income (Loss) [Member]
Noncontrolling Interest [Line Items]
Balance				(221.1)
Net income				0.0
Other comprehensive income (loss)				27.4
Dividends declared				0.0
Dividends to non-controlling interest				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Balance		(193.7)		(193.7)
Treasury Stock [Member]
Noncontrolling Interest [Line Items]
Balance				(596.3)
Net income				0.0
Other comprehensive income (loss)				0.0
Dividends declared				0.0
Dividends to non-controlling interest				0.0
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Balance		(596.3)		(596.3)
Non-controlling Interests [Member]
Noncontrolling Interest [Line Items]
Balance				24.4
Net income				1.8
Other comprehensive income (loss)				0.9
Dividends declared				0.0
Dividends to non-controlling interest				(1.7)
Issuance of shares pursuant to employee stock compensation plans				0.0
Stock based compensation				0.0
Balance		$ 25.4		$ 25.4

[1] Condensed from audited financial statements

[2] Unaudited