Allocation by Investment Type (Detail)	Sep. 28, 2018	Sep. 29, 2017
Retirement Benefits
Actual, Allocation Percentage	100.00%	100.00%
Equity Securities
Retirement Benefits
Actual, Allocation Percentage	59.50%	58.40%
Equity Securities | Minimum
Retirement Benefits
Target, Allocation Percentage	35.00%
Equity Securities | Maximum
Retirement Benefits
Target, Allocation Percentage	70.00%
Debt Securities
Retirement Benefits
Actual, Allocation Percentage	33.90%	35.30%
Debt Securities | Minimum
Retirement Benefits
Target, Allocation Percentage	30.00%
Debt Securities | Maximum
Retirement Benefits
Target, Allocation Percentage	65.00%
Cash
Retirement Benefits
Target, Allocation Percentage	0.00%
Actual, Allocation Percentage	6.60%	6.30%