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Pension and Other Employee Benefits - Schedule of Weighted-Average Net Periodic Benefit Cost Assumptions (Detail)
12 Months Ended
Sep. 30, 2017
Sep. 24, 2016
Sep. 26, 2015
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]      
Discount rate 2.15% 1.30% 2.05%
Expected return on plan assets 0.00% 0.00% 0.00%
Rate of compensation increase 0.00% 0.00% 0.00%