Loss Per Share - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 03, 2021	Dec. 31, 2020	Jun. 15, 2020	Apr. 21, 2020
Class of Stock [Line Items]
Warrants recorded within stockholders' equity	$ 47
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Proceeds from the issuance of common stock	$ 500
2020 ATM Offering
Class of Stock [Line Items]
Number of shares issuable (in shares)				28,000,000
Common stock, par value (in dollars per share)					$ 0.01
Number of shares issued (in shares)	7,000,000
Sale price (in dollars per share)	$ 42.98
Proceeds from the issuance of common stock	$ 282
2021 ATM Offering
Class of Stock [Line Items]
Number of shares issuable (in shares)		37,000,000
Common stock, par value (in dollars per share)		$ 0.01
Number of shares issued (in shares)	4,000,000
Sale price (in dollars per share)	$ 57.50
Proceeds from the issuance of common stock	$ 250
Payroll Support Program 2 (PSP2) Warrants
Class of Stock [Line Items]
Warrants to purchase securities (in shares)	1,700,000
Warrant exercise price (in dollars per share)	$ 43.26
Warrant term	5 years
Warrants recorded within stockholders' equity	$ 47