Restructuring and Severance Charges - Restructuring Activities and Accrued Liabilities (Details) $ in Millions	6 Months Ended
	Apr. 03, 2016 USD ($)
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 6.2
Assumed from acquisition	3.0
Provisions	53.6
Reversal of prior provision	(0.2)
Cash expenditures	(23.7)
Other non-cash settlement	(26.0)
Ending Balance	12.9
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	48.7
Restructuring Reserve [Roll Forward]
Beginning Balance	2.9
Assumed from acquisition	3.0
Provisions	48.9
Reversal of prior provision	(0.2)
Cash expenditures	(21.7)
Other non-cash settlement	(23.3)
Ending Balance	9.6
Contract Termination Costs
Restructuring Reserve [Roll Forward]
Beginning Balance	3.2
Assumed from acquisition	0.0
Provisions	1.9
Reversal of prior provision	0.0
Cash expenditures	(1.6)
Other non-cash settlement	(0.3)
Ending Balance	3.2
Other Associated Costs
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	2.8
Restructuring Reserve [Roll Forward]
Beginning Balance	0.1
Assumed from acquisition	0.0
Provisions	2.8
Reversal of prior provision	0.0
Cash expenditures	(0.4)
Other non-cash settlement	(2.4)
Ending Balance	0.1
PMC-SIERRA INC. | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	46.7
PMC-SIERRA INC. | Other Associated Costs
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 2.4