Fair value measurements - level 3 roll (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 02, 2016	Mar. 28, 2015	Jun. 27, 2015
Public bonds and private placement [Member] | Fair value, inputs, level 1 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, fair value disclosure	$ 5,100.0		$ 3,800.0
Contingent Consideration Classified as Equity [Member] | Fair value, inputs, level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	17.9
Net realized losses	0.3	$ 0.0
Purchases or additions	29.5	0.0
Foreign currency effect	0.3	0.0
Ending balance	48.0	$ 12.4
Fair value, measurements, recurring [Member] | Fair value, inputs, level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 17.9