SEGMENT INFORMATION - Operating Results Information for Each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 29, 2017	Dec. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 678.5	$ 601.5
Operating Earnings (Loss)	121.4	17.4
Oncology Systems
Segment Reporting Information [Line Items]
Revenues	649.4	571.2
Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues	29.1	30.3
Unallocated corporate
Segment Reporting Information [Line Items]
Operating Earnings (Loss)	(1.6)	(48.4)
Operating Segments
Segment Reporting Information [Line Items]
Operating Earnings (Loss)	123.0	65.8
Operating Segments | Oncology Systems
Segment Reporting Information [Line Items]
Revenues	649.4	571.2
Operating Earnings (Loss)	138.2	116.1
Operating Segments | Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues	29.1	30.3
Operating Earnings (Loss)	$ (15.2)	$ (50.3)