v3.20.1
Stockholder's Equity - SAR and Option Activity (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Share-Based Compensation Arrangement By Share-Based Payment Award, Options And Equity Instruments Other Than Options, Nonvested, Number Of Shares [Abstract]    
Weighted-Average Exercise Price Per Share, Outstanding (in dollars per share) $ 9.79  
Weighted-Average Exercise Price Per Share, Awards granted (in dollars per share) 11.55  
Weighted-Average Exercise Price Per Share, Awards exercised (in dollars per share) 3.06  
Weighted-Average Exercise Price Per Share, Awards canceled and forfeited (in dollars per share) 21.14  
Weighted-Average Exercise Price Per Share, Outstanding (in dollars per share) 10.72 $ 9.79
Weighted-Average Exercise Price Per Share, Vested and expected to vest (in dollars per share) 5.41  
Weighted-Average Exercise Price Per Share, Exercisable (in dollars per share) $ 5.41  
Share-Based Compensation Arrangement By Share-based Payment Award, Options And Equity Instruments Other Than Options, Nonvested, Additional Disclosures [Abstract]    
Weighted-Average Contractual Life, Outstanding 4 years 8 months 4 days 4 years 9 months
Weighted-Average Contractual Life, Vested and expected to vest 4 years 3 months 21 days  
Weighted-Average Contractual Life, Exercisable 4 years 3 months 21 days  
Aggregate Intrinsic Value, Outstanding $ 599 $ 746
Aggregate Intrinsic Value, Vested and expected to vest 585  
Aggregate Intrinsic Value, Exercisable $ 585  
SARs    
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]    
Shares outstanding (in shares) 337  
Awards granted (in shares) 0  
Awards exercised (in shares) (2)  
Awards canceled and forfeited (in shares) (24)  
Shares outstanding (in shares) 311 337
Vested and expected to vest (in shares) 198  
Exercisable (in shares) 198  
Stock options    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]    
Options outstanding (in shares) 34,801  
Awards granted (in shares) 1,194  
Awards exercised (in shares) (4,490)  
Awards canceled and forfeited (in shares) (220)  
Options outstanding (in shares) 31,285 34,801
Vested and expected to vest (in shares) 25,331  
Exercisable (in shares) 25,331