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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 |  |

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