Fair Value Measurements - Narrative (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2021 USD ($) $ / shares	Jun. 30, 2021 USD ($) $ / shares	Dec. 31, 2020 USD ($)	May 01, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Initial conversion price (in USD per share) | $ / shares	$ 38.48	$ 38.48
Amortization period (in years)	5 years
1.250 Convertible Senior Notes due 2025 | Convertible Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount				$ 2,300,000,000
Stated interest rate	1.25%	1.25%		1.25%
Initial conversion ratio	0.0259909
Initial conversion price (in USD per share) | $ / shares	$ 38.48	$ 38.48
Face amount of convertible notes	$ 403,000,000	$ 403,000,000	$ 403,000,000
Effective interest rate	5.20%	5.20%
Interest expense	$ 28,000,000	$ 56,000,000
If-converted value in excess of principal amount	874,000,000
1.250 Convertible Senior Notes due 2025 | Convertible Debt | Non-Cash Amortization of Debt Discount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest expense	19,000,000	37,000,000
1.250 Convertible Senior Notes due 2025 | Convertible Debt | Non-Cash Amortization of Debt Issuance Costs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest expense	2,000,000	4,000,000
1.250 Convertible Senior Notes due 2025 | Convertible Debt | Contractual Coupon Interest Expense
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest expense	$ 7,000,000	$ 15,000,000