SEGMENT INFORMATION - Operating Results Information for Each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jul. 01, 2016	Jun. 30, 2017	Jul. 01, 2016
Segment Reporting Information [Line Items]
Revenues	$ 662.4	$ 642.9	$ 1,929.2	$ 1,873.9
Operating Earnings (Loss)	116.3	102.1	232.2	293.4
Unallocated corporate
Segment Reporting Information [Line Items]
Operating Earnings (Loss)	(3.4)	(15.3)	(64.8)	(28.8)
Operating Segments
Segment Reporting Information [Line Items]
Revenues	662.4	642.7	1,929.2	1,873.6
Operating Earnings (Loss)	119.7	119.1	297.0	326.4
Operating Segments | Oncology Systems
Segment Reporting Information [Line Items]
Revenues	594.0	605.4	1,799.2	1,779.0
Operating Earnings (Loss)	132.1	131.7	379.5	363.2
Operating Segments | Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues	68.4	37.3	130.0	94.6
Operating Earnings (Loss)	(12.4)	(12.6)	(82.5)	(36.8)
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	0.0	0.2	0.0	0.3
Operating Earnings (Loss)	$ 0.0	$ (1.7)	$ 0.0	$ (4.2)