CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Class A Stock	Common Stock	Restricted stock
Beginning Balance (in shares) at Dec. 31, 2015					3.6	1.9	106.4
Beginning Balance at Dec. 31, 2015	$ 3,654.8	$ 3,099.5	$ 852.7	$ 8.6	$ (306.1)	$ 0.0	$ 0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options (in shares)							1.7
Issuance of Common Stock in connection with exercise of stock options	115.2	115.2					$ 0.0
Common Stock tendered upon exercise of stock options and vesting of restricted stock in connection with employee tax obligations (in shares)							(0.3)
Common Stock tendered upon exercise of stock options and vesting of restricted stock in connection with employee tax obligations	(143.2)	(143.2)
Issuance of Common Stock in connection with conversion of convertible notes (in shares)							0.1
Issuance of Common Stock in connection with conversion of convertible notes	48.0	48.0
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (in shares)							0.0
Issuance of Common Stock in connection with Company 401(k) Savings Plan	16.6	16.6
Stock-based compensation charges	574.9	574.9
Acquisition of Common Stock (in shares)					(0.2)
Acquisition of Common Stock	0.0	10.1			$ (10.1)
Reduction of warrants	(643.3)	(643.3)
Reduction of equity component of convertible notes	(47.8)	(47.8)
Net income	895.5		895.5
Other comprehensive loss, net of tax	(21.4)			(21.4)
Ending Balance (in shares) at Dec. 31, 2016					3.8	1.9	107.9
Ending Balance at Dec. 31, 2016	4,449.3	3,030.0	1,748.2	(12.8)	$ (316.2)	$ 0.0	$ 0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options (in shares)							2.3
Issuance of Common Stock in connection with exercise of stock options	240.6	240.6					$ 0.0
Common Stock tendered upon exercise of stock options and vesting of restricted stock in connection with employee tax obligations (in shares)							(0.8)
Common Stock tendered upon exercise of stock options and vesting of restricted stock in connection with employee tax obligations	(301.7)	(301.7)
Issuance of restricted stock under Long-Term Incentive Plan (in shares)								0.1
Issuance of restricted stock under Long-Term Incentive Plan	0.0
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (in shares)							0.0
Issuance of Common Stock in connection with Company 401(k) Savings Plan	19.4	19.4
Stock-based compensation charges	524.6	524.6
Net income	1,198.5		1,198.5
Other comprehensive loss, net of tax	13.4			13.4
Ending Balance (in shares) at Dec. 31, 2017					3.8	1.9	109.5
Ending Balance at Dec. 31, 2017	6,144.1	3,512.9	2,946.7	0.6	$ (316.2)	$ 0.0	$ 0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock in connection with exercise of stock options (in shares)							1.7
Issuance of Common Stock in connection with exercise of stock options	114.2	114.2					$ 0.0
Common Stock tendered upon exercise of stock options and vesting of restricted stock in connection with employee tax obligations (in shares)							(0.5)
Common Stock tendered upon exercise of stock options and vesting of restricted stock in connection with employee tax obligations	(187.2)	(187.2)
Issuance of restricted stock under Long-Term Incentive Plan (in shares)								0.3
Issuance of restricted stock under Long-Term Incentive Plan	0.0
Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (in shares)							0.1
Issuance of Common Stock in connection with Company 401(k) Savings Plan	26.9	26.9
Stock-based compensation charges	444.8	444.8
Acquisition of Common Stock (in shares)					(0.2)
Acquisition of Common Stock	(80.2)				$ (80.2)
Change in accounting standards | Accounting Standards Update 2014-09 And 2016-01	(143.4)		(136.8)
Change in accounting standards | Accounting Standards Update 2016-01				(6.6)
Net income	2,444.4		2,444.4
Other comprehensive loss, net of tax	(6.3)			(6.3)
Ending Balance (in shares) at Dec. 31, 2018					4.0	1.9	111.1
Ending Balance at Dec. 31, 2018	$ 8,757.3	$ 3,911.6	$ 5,254.3	$ (12.3)	$ (396.4)	$ 0.0	$ 0.1