Statement of Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock at Cost [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings
Balances, common shares at Dec. 31, 2016		231.9
Balances, treasury shares at Dec. 31, 2016				8.0
Balances, value at Dec. 31, 2016	$ 8,693.8	$ 0.0	$ 7,957.0	$ (1,141.3)	$ 60.5	$ 1,817.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common stock, shares				4.0
Repurchase of common stock value	(463.6)			$ (463.6)
Issuance of common stock from exercise of options, shares		1.3
Issuance of common stock from exercise of options, value	85.9		85.9
Issuance of restricted common stock, shares		1.1
Share-based compensation expense, value	247.4		247.4
Net income (loss)	443.3					443.3
Other comprehensive income (loss)	(94.9)				(94.9)
Balances, common shares at Dec. 31, 2017		234.3
Balances, treasury shares at Dec. 31, 2017				12.0
Balances, value at Dec. 31, 2017	8,893.1	$ 0.0	8,290.3	$ (1,604.9)	(34.4)	2,242.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new guidance, value	(18.8)					(18.8)
Repurchase of common stock, shares		0.0		0.7
Repurchase of common stock value	(85.0)			$ (85.0)
Issuance of common stock from exercise of options, shares		0.6
Issuance of common stock from exercise of options, value	47.6		47.6
Issuance of restricted common stock, shares		1.3
Issuance of restricted common stock	(0.3)		(0.3)
Share-based compensation expense, value	201.5		201.5
Net income (loss)	77.6					77.6
Other comprehensive income (loss)	$ 24.7				24.7
Balances, common shares at Dec. 31, 2018		236.2
Balances, treasury shares at Dec. 31, 2018	12.7			12.7
Balances, value at Dec. 31, 2018	$ 9,165.3	$ 0.0	8,539.1	$ (1,689.9)	(9.7)	2,325.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new guidance, value	6.1					6.1
Repurchase of common stock, shares				3.8
Repurchase of common stock value	$ (416.0)			$ (416.0)
Issuance of common stock from exercise of options, shares	0.3	0.4
Issuance of common stock from exercise of options, value	$ 29.9		29.9
Issuance of restricted common stock, shares		1.2
Issuance of restricted common stock	0.0		0.0
Share-based compensation expense, value	235.7		235.7
Net income (loss)	2,404.3					2,404.3
Other comprehensive income (loss)	$ (57.1)				(57.1)
Balances, common shares at Dec. 31, 2019		237.8
Balances, treasury shares at Dec. 31, 2019	16.5			16.5
Balances, value at Dec. 31, 2019	$ 11,271.8	$ 0.0	$ 8,804.7	$ (2,105.9)	$ (66.8)	4,639.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new guidance, value	$ (90.3)					$ (90.3)