Acquisitions, Goodwill and Intangible Assets (Changes in the carrying amount of goodwill) (Details)
$ in Millions
6 Months Ended
Mar. 31, 2017
USD ($)
Goodwill  
Goodwill beginning balance $ 1,919
Foreign currency translation adjustments (3)
Goodwill ending balance 1,928
Commercial Systems [Member]  
Goodwill  
Goodwill beginning balance 326
Pulse.aero acquisition 0
Foreign currency translation adjustments (1)
Goodwill ending balance 325
Government Systems [Member]  
Goodwill  
Goodwill beginning balance 503
Pulse.aero acquisition 0
Foreign currency translation adjustments (3)
Goodwill ending balance 500
Information Management Services [Member]  
Goodwill  
Goodwill beginning balance 1,090
Foreign currency translation adjustments 1
Goodwill ending balance 1,103
Pulse.aero [Member]  
Goodwill  
Pulse.aero acquisition 12
Pulse.aero [Member] | Information Management Services [Member]  
Goodwill  
Pulse.aero acquisition $ 12