Fair Value Measurements - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions		Sep. 26, 2020	Dec. 31, 2019
Measured at fair value on a non-recurring basis:
Goodwill carrying amount		$ 3,839.3	$ 4,116.7
Definite-lived intangible assets carrying value		2,895.4	2,921.2
Measured at fair value on a recurring basis | Level 1
Assets:
Investment securities		3.3	6.6
Foreign currency forward contracts		0.0	0.0
Cross-currency swap		0.0	0.0
Funds associated with Israeli severance liability		0.0	0.0
Royalty Pharma contingent milestone		0.0	0.0
Total assets		3.3	6.6
Liabilities:
Foreign currency forward contracts		0.0	0.0
Contingent consideration		0.0	0.0
Total liabilities		0.0	0.0
Measured at fair value on a recurring basis | Level 2
Assets:
Investment securities		0.0	0.0
Foreign currency forward contracts		8.7	4.3
Cross-currency swap		7.7	26.3
Funds associated with Israeli severance liability		14.2	14.6
Royalty Pharma contingent milestone		0.0	0.0
Total assets		30.6	45.2
Liabilities:
Foreign currency forward contracts		8.8	8.4
Contingent consideration		0.0	0.0
Total liabilities		8.8	8.4
Measured at fair value on a recurring basis | Level 3
Assets:
Investment securities		0.0	0.0
Foreign currency forward contracts		0.0	0.0
Cross-currency swap		0.0	0.0
Funds associated with Israeli severance liability		0.0	0.0
Royalty Pharma contingent milestone		121.2	95.3
Total assets		121.2	95.3
Liabilities:
Foreign currency forward contracts		0.0	0.0
Contingent consideration		12.8	11.9
Total liabilities		12.8	11.9
Measured at fair value on a non-recurring basis
Measured at fair value on a non-recurring basis:
Definite-lived intangible assets carrying value			55.3
Measured at fair value on a non-recurring basis | Level 1
Assets:
Total assets		0.0	0.0
Measured at fair value on a non-recurring basis:
Goodwill	[1]	0.0	0.0
Definite-lived intangible assets	[2]	0.0	0.0
Measured at fair value on a non-recurring basis | Level 2
Assets:
Total assets		0.0	0.0
Measured at fair value on a non-recurring basis:
Goodwill	[1]	0.0	0.0
Definite-lived intangible assets	[2]	0.0	0.0
Measured at fair value on a non-recurring basis | Level 3
Assets:
Total assets		811.1	1,036.4
Measured at fair value on a non-recurring basis:
Goodwill	[1]	811.1	1,013.1
Definite-lived intangible assets	[2]	0.0	23.3
RX
Measured at fair value on a non-recurring basis:
Goodwill carrying amount	[3]	811.1	1,013.9
RX | Measured at fair value on a non-recurring basis
Measured at fair value on a non-recurring basis:
Goodwill carrying amount		$ 1,013.5	$ 1,122.3

[1] During the three months ended September 26, 2020, goodwill with a carrying amount of $1,013.5 million was written down to a fair value of $811.1 million. During the year ended December 31, 2019, goodwill with a carrying amount of $1,122.3 million was written down to a fair value of $1,013.1 million.

[2] During the year ended December 31, 2019, definite-lived intangible assets with a carrying amount of $55.3 million were written down to a fair value of $23.3 million.

[3] We had accumulated goodwill impairments of $109.2 million and $311.6 million as of December 31, 2019 and September 26, 2020