Condensed Consolidated Statements of Changes in Stockholder's Equity Statement - USD ($) shares in Millions, $ in Millions	Total	Adoption of new accounting standards	Common Stock	Additional Paid-In Capital	Treasury Stock at Cost	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Adoption of new accounting standards
Balances, common shares at Dec. 31, 2018			236.2
Balances, value at Dec. 31, 2018	$ 9,165.3	$ (90.3)	$ 0.0	$ 8,539.1	$ (1,689.9)	$ (9.7)	$ 2,325.8	$ (90.3)
Balances, treasury shares at Dec. 31, 2018					12.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common stock, shares	3.5				3.5
Repurchase of common stock	$ (383.5)				$ (383.5)
Issuance of common stock under stock option and stock purchase plans, shares			0.3
Issuance of common stock under stock option and stock purchase plans	23.2			23.2
Issuance of restricted common stock, shares			1.0
Issuance of restricted common stock	0.0
Share-based compensation expense	175.7			175.7
Net income	1,515.3						1,515.3
Other comprehensive income	(38.5)					(38.5)
Balances, treasury shares at Sep. 30, 2019					16.2
Balances, value at Sep. 30, 2019	10,367.2		$ 0.0	8,738.0	$ (2,073.4)	(48.2)	3,750.8
Balances, common shares at Sep. 30, 2019			237.5
Balances, common shares at Jun. 30, 2019			237.3
Balances, value at Jun. 30, 2019	$ 10,163.5		$ 0.0	8,677.0	$ (1,738.8)	(57.9)	3,283.2
Balances, treasury shares at Jun. 30, 2019					13.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common stock, shares	3.1				3.1
Repurchase of common stock	$ (334.6)				$ (334.6)
Issuance of common stock under stock option and stock purchase plans, shares			0.1
Issuance of common stock under stock option and stock purchase plans	1.9			1.9
Issuance of restricted common stock, shares			0.1
Issuance of restricted common stock	0.0
Share-based compensation expense	59.1			59.1
Net income	467.6						467.6
Other comprehensive income	9.7					9.7
Balances, treasury shares at Sep. 30, 2019					16.2
Balances, value at Sep. 30, 2019	10,367.2		$ 0.0	8,738.0	$ (2,073.4)	(48.2)	3,750.8
Balances, common shares at Sep. 30, 2019			237.5
Balances, common shares at Dec. 31, 2019			237.8
Balances, value at Dec. 31, 2019	$ 11,271.8		$ 0.0	8,804.7	$ (2,105.9)	(66.8)	4,639.8
Balances, treasury shares at Dec. 31, 2019	16.5				16.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common stock, shares	4.2				4.2
Repurchase of common stock	$ (434.3)				$ (434.3)
Issuance of common stock under stock option and stock purchase plans, shares			0.4
Issuance of common stock under stock option and stock purchase plans	23.4			23.4
Issuance of restricted common stock, shares			1.5
Issuance of restricted common stock	0.0
Share-based compensation expense	191.6			195.1	$ (3.5)
Portola replacement equity awards attributable to the pre-combination period	7.2			7.2
Net income	67.6						67.6
Other comprehensive income	$ (52.4)					(52.4)
Balances, treasury shares at Sep. 30, 2020	20.7				20.7
Balances, value at Sep. 30, 2020	$ 11,074.9		$ 0.0	9,030.4	$ (2,543.7)	(119.2)	4,707.4
Balances, common shares at Sep. 30, 2020			239.7
Balances, common shares at Jun. 30, 2020			239.2
Balances, value at Jun. 30, 2020	$ 10,490.8		$ 0.0	8,942.4	$ (2,470.0)	(110.9)	4,129.3
Balances, treasury shares at Jun. 30, 2020					20.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common stock, shares	0.6				0.6
Repurchase of common stock	$ (73.5)				$ (73.5)
Issuance of common stock under stock option and stock purchase plans, shares			0.2
Issuance of common stock under stock option and stock purchase plans	10.5			10.5
Issuance of restricted common stock, shares			0.3
Issuance of restricted common stock	0.0
Share-based compensation expense	70.1			70.3	$ (0.2)
Portola replacement equity awards attributable to the pre-combination period	7.2			7.2
Net income	578.1						578.1
Other comprehensive income	$ (8.3)					(8.3)
Balances, treasury shares at Sep. 30, 2020	20.7				20.7
Balances, value at Sep. 30, 2020	$ 11,074.9		$ 0.0	$ 9,030.4	$ (2,543.7)	$ (119.2)	$ 4,707.4
Balances, common shares at Sep. 30, 2020			239.7