Receivables - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 30, 2016	Sep. 29, 2017	Sep. 30, 2016	Oct. 02, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled receivables		$ 124.4	$ 111.6
Allowance for doubtful accounts		63.1	24.2
Unbilled long-term receivables			37.9
Accounts receivable, allowance for doubtful accounts		45.9	24.2
Allowance, noncurrent		17.2
Provision for doubtful accounts receivable	$ 37.8	43.7	$ 3.5	$ 1.1
Unbilled Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts		$ 17.2
Original CPTC loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	34.2
Provision for doubtful accounts receivable	34.2
Original CPTC loans | Unbilled Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for doubtful accounts receivable	$ 17.2