Business Segment Information - Sales and Earnings of Operating Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Sales	$ 2,011	$ 1,193
Income before income taxes	257	203
Interest expense	(64)	(20)
Stock-based compensation	(9)	(6)
Transaction and integration costs	(27)	(11)
Income tax benefit (expense)	23	(58)
Net income	280	145
B/E Aerospace
Segment Reporting Information [Line Items]
Transaction and integration costs	(17)	(11)
Bridge facility fees included in interest expense	0	3
Transaction, integration and financing costs	17	14
B/E Aerospace | Bridge Facility
Segment Reporting Information [Line Items]
Bridge facility fees included in interest expense		3
Merger Agreement with UTC
Segment Reporting Information [Line Items]
Transaction and integration costs	(10)
Interior Systems
Segment Reporting Information [Line Items]
Sales	656	0
Commercial Systems
Segment Reporting Information [Line Items]
Sales	608	549
Government Systems
Segment Reporting Information [Line Items]
Sales	573	475
Information Management Services
Segment Reporting Information [Line Items]
Sales	174	169
Operating Segments
Segment Reporting Information [Line Items]
Income before income taxes	371	251
Operating Segments | Interior Systems
Segment Reporting Information [Line Items]
Income before income taxes	94	0
Operating Segments | Commercial Systems
Segment Reporting Information [Line Items]
Income before income taxes	139	125
Operating Segments | Government Systems
Segment Reporting Information [Line Items]
Income before income taxes	109	96
Operating Segments | Information Management Services
Segment Reporting Information [Line Items]
Income before income taxes	29	30
Segment Reconciling Items
Segment Reporting Information [Line Items]
Interest expense	(64)	(20)
Stock-based compensation	(9)	(6)
General corporate, net	(14)	(11)
Transaction and integration costs	$ (27)	$ (11)