Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 29, 2018
Net income (loss)	$ 1,110.5	$ (203.6)	$ (111.3)
Changes in foreign currency translation adjustment	18.5	(14.8)	(8.1)
Loss (gain) reclassified from accumulated other comprehensive income (loss) to the statement of operations	0.0	0.0	0.4
Changes in pension plans, net of taxes of $0.1 in 2020, $0.3 in 2019, and $(0.6) in 2018	(0.1)	(0.6)	0.5
(Loss) gain recognized, net of tax of $(8.3) million in 2020 and $1.2 million in 2019 for interest rate swaps	(0.5)	(8.0)
Loss recognized in other comprehensive income (loss), net	(28.1)	(4.5)	(5.7)
Loss reclassified from accumulated other comprehensive loss to the statement of operations, net	2.3	3.1	3.6
Other comprehensive loss	(7.4)	(16.8)	(9.3)
Comprehensive income (loss)	1,103.1	(220.4)	(120.6)
Net loss attributable to noncontrolling interest	4.7	0.0	0.0
Comprehensive loss attributable to noncontrolling interest	4.7	0.0	0.0
Comprehensive income (loss) attributable to Hologic	1,107.8	(220.4)	(120.6)
Interest Rate Swap [Member]
(Loss) gain recognized, net of tax of $(8.3) million in 2020 and $1.2 million in 2019 for interest rate swaps	(27.6)	3.5	0.0
Interest rate caps - derivative
Loss recognized in other comprehensive income (loss), net	$ (0.5)	$ (8.0)	$ (5.7)