Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands	Total	Share Repurchase Program [Member]	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]	Treasury Stock [Member] Share Repurchase Program [Member]	Noncontrolling Interest
Balance (in shares) at Sep. 30, 2017			287,853				12,560
Balance at Sep. 30, 2017	$ 2,784,700,000		$ 2,900,000	$ 5,630,800,000	$ (2,382,700,000)	$ (16,200,000)	$ (450,100,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			795
Exercise of stock options	17,300,000			17,300,000
Vesting of restricted stock units, net of shares withheld for employee taxes (in shares)			804
Vesting of restricted stock units, net of shares withheld for employee taxes	(16,700,000)			(16,700,000)
Common stock issued under the employee stock purchase plan (in shares)			448
Common stock issued under the employee stock purchase plan	15,600,000			15,600,000
Stock-based compensation expense	65,000,000.0			65,000,000.0
Repurchase of common stock (in shares)							7,252
Repurchase of common stock	(275,800,000)						$ (275,800,000)
Reacquisition of equity component from convertible notes repurchase, net of taxes	(40,700,000)			(40,700,000)
Foreign currency translation adjustment	(8,100,000)					(8,100,000)
Adjustment to minimum pension liability, net	500,000					500,000
Unrealized losses on derivatives, net of taxes	(5,700,000)					(5,700,000)
Loss reclassified from accumulated other comprehensive loss to the statement of operations, net	3,600,000					3,600,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	400,000					400,000
Net income (loss) attributable to Hologic	(111,300,000)				(111,300,000)
Payments to Noncontrolling Interests	0
Balance (in shares) at Sep. 29, 2018			289,900				19,812
Balance at Sep. 29, 2018	2,428,800,000		$ 2,900,000	5,671,300,000	(2,494,000,000.0)	(25,500,000)	$ (725,900,000)		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting standard transition adjustment - ASC 606	6,400,000				6,400,000
Accounting standard transition adjustment - ASU 2016-16	2,500,000				2,500,000
Exercise of stock options (in shares)			1,304
Exercise of stock options	32,800,000			32,800,000
Vesting of restricted stock units, net of shares withheld for employee taxes (in shares)			645
Vesting of restricted stock units, net of shares withheld for employee taxes	(12,800,000)			(12,800,000)
Common stock issued under the employee stock purchase plan (in shares)			474
Common stock issued under the employee stock purchase plan	16,500,000			16,500,000
Stock-based compensation expense	62,000,000.0			62,000,000.0
Repurchase of common stock (in shares)							4,826
Repurchase of common stock	(200,100,000)						$ (200,100,000)
Foreign currency translation adjustment	(14,800,000)					(14,800,000)
Adjustment to minimum pension liability, net	(600,000)					(600,000)
Unrealized losses on derivatives, net of taxes	(8,000,000.0)					(8,000,000.0)
Unrealized gain on interest rate swap	3,500,000					3,500,000
Loss reclassified from accumulated other comprehensive loss to the statement of operations, net	3,100,000					3,100,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0
Net income (loss) attributable to Hologic	(203,600,000)				(203,600,000)
Payments to Noncontrolling Interests	0
Balance (in shares) at Sep. 28, 2019			292,323				24,638
Balance at Sep. 28, 2019	$ 2,115,700,000		$ 2,900,000	5,769,800,000	(2,688,700,000)	(42,300,000)	$ (926,000,000.0)		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,800		1,761
Exercise of stock options	$ 48,300,000			48,300,000
Vesting of restricted stock units, net of shares withheld for employee taxes (in shares)			611
Vesting of restricted stock units, net of shares withheld for employee taxes	(14,200,000)			(14,200,000)
Common stock issued under the employee stock purchase plan (in shares)			412
Common stock issued under the employee stock purchase plan	17,600,000			17,600,000
Stock-based compensation expense	83,300,000			83,300,000
Repurchase of common stock (in shares)							9,064	3,907
Repurchase of common stock	(448,600,000)	$ (205,000,000.0)					$ (448,600,000)	$ (205,000,000.0)
Foreign currency translation adjustment	18,500,000					18,500,000
Adjustment to minimum pension liability, net	(100,000)					(100,000)
Unrealized losses on derivatives, net of taxes	(500,000)					(500,000)
Unrealized gain on interest rate swap	(27,600,000)					(27,600,000)
Loss reclassified from accumulated other comprehensive loss to the statement of operations, net	2,300,000					2,300,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0
Net income (loss) attributable to Hologic	1,110,500,000				1,115,200,000				(4,700,000)
Payments to Noncontrolling Interests	(1,800,000)								(1,800,000)
Noncontrolling Interest, Increase from Business Combination	8,600,000								8,600,000
Balance (in shares) at Sep. 26, 2020			295,107				37,609
Balance at Sep. 26, 2020	2,707,300,000		$ 2,900,000	$ 5,904,800,000	(1,573,200,000)	$ (49,700,000)	$ (1,579,600,000)		$ 2,100,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting standard transition adjustment | Accounting Standards Update 2018-01 [Member]	$ 300,000				$ 300,000