SEGMENT INFORMATION - Operating Results Information for Each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 30, 2018	Mar. 31, 2017	Mar. 30, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 729.9	$ 663.2	$ 1,408.4	$ 1,264.7
Operating Earnings (Loss)	94.3	90.1	215.7	107.5
Oncology Systems
Segment Reporting Information [Line Items]
Revenues	698.0	631.9	1,347.4	1,203.1
Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues	31.9	31.3	61.0	61.6
Unallocated corporate
Segment Reporting Information [Line Items]
Operating Earnings (Loss)	(31.3)	(13.0)	(32.9)	(61.4)
Operating Segments
Segment Reporting Information [Line Items]
Operating Earnings (Loss)	125.6	103.1	248.6	168.9
Operating Segments | Oncology Systems
Segment Reporting Information [Line Items]
Revenues	698.0	631.9	1,347.4	1,203.1
Operating Earnings (Loss)	143.1	122.9	281.3	239.0
Operating Segments | Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues	31.9	31.3	61.0	61.6
Operating Earnings (Loss)	$ (17.5)	$ (19.8)	$ (32.7)	$ (70.1)