Allocation by Investment Type (Detail)	Sep. 29, 2017	Sep. 30, 2016
Retirement Benefits
Actual, Allocation Percentage	100.00%	100.00%
Equity Securities
Retirement Benefits
Actual, Allocation Percentage	58.40%	56.40%
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	35.30%	37.10%
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	6.30%	6.50%