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Net Loss per Share - Narrative (Details) shares in Millions					3 Months Ended
Net Loss per Share - Narrative (Details) shares in Millions	Aug. 19, 2019 $ / shares shares	Nov. 19, 2018 $ / shares shares	Sep. 15, 2017 $ / shares shares	Sep. 11, 2017 $ / shares shares	Mar. 31, 2020 shares	Mar. 31, 2019 shares	Aug. 14, 2019 $ / shares	Nov. 14, 2018 $ / shares
Class of Stock [Line Items]
Allocation of undistributed earnings between stock classes, conversion ratio					1
0.375% 2017 Senior Notes due 2022 \| Convertible Debt
Class of Stock [Line Items]
Conversion price (in usd per share) \| $ / shares			$ 104.06
0.375% 2017 Senior Notes due 2022 \| Convertible Debt \| Class A common stock
Class of Stock [Line Items]
Conversion of stock, shares issued (in shares)			4.1
Cap price, per share (in usd per share) \| $ / shares				$ 154.16
Capped call transaction, shares issued (in shares)				2.8
1.125% 2018 Senior Notes Due 2024 \| Convertible Debt \| Class A common stock
Class of Stock [Line Items]
Conversion price (in usd per share) \| $ / shares		$ 116.40
Conversion of stock, shares issued (in shares)		4.9
Cap price, per share (in usd per share) \| $ / shares		$ 219.63						$ 219.63
Capped call transaction, shares issued (in shares)		2.6
1.00% 2019 Senior Notes Due 2026 \| Convertible Debt \| Class A common stock
Class of Stock [Line Items]
Conversion price (in usd per share) \| $ / shares	$ 148.48
Conversion of stock, shares issued (in shares)	6.4
Cap price, per share (in usd per share) \| $ / shares	$ 280.15						$ 280.15
Capped call transaction, shares issued (in shares)	3.4
Common Stock Options, Restricted Stock Options And Restricted Stock Units
Class of Stock [Line Items]
Antidilutive securities excluded from diluted earnings per share calculation (in shares)					7.2	8.0