Description of Business and Basis of Presentation (Revenues Realized from Each of These Types of Contracts) (Details) - Business	3 Months Ended	12 Months Ended
	Apr. 01, 2016	Sep. 29, 2017	Sep. 30, 2016	Oct. 02, 2015
Basis of Presentation [Line Items]
Cost-reimbursable		81.00%	82.00%	83.00%
Fixed-price		19.00%	18.00%	17.00%
Number of operating and reporting structure of business	4
Minimum
Basis of Presentation [Line Items]
Frequency of fiscal year with an additional week of activity (in years)		5 years
Maximum
Basis of Presentation [Line Items]
Frequency of fiscal year with an additional week of activity (in years)		6 years