Borrowings and Credit Arrangements - Interest Expense under Convertible Notes (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Mar. 28, 2015
Mar. 29, 2014
Mar. 28, 2015
Mar. 29, 2014
Debt Conversion [Line Items]        
Non-cash interest expense     $ 33.2 $ 35.8
Convertible Notes Payable        
Debt Conversion [Line Items]        
Amortization of debt discount 9.0 8.3 17.8 19.9
Amortization of deferred financing costs 0.4 0.4 0.9 1.0
Principal accretion 4.0 3.8 7.9 7.6
Non-cash interest expense 13.4 12.5 26.6 28.5
2.00% accrued interest (cash) 4.8 4.8 9.5 12.9
Convertible Notes Interest Expense 2.00% 2.00% 2.00% 2.00%
Interest expense, net $ 18.2 $ 17.3 $ 36.1 $ 41.4