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Earnings per Share - Additional information (Details) - USD ($)
$ / shares in Units, $ in Millions
1 Months Ended 3 Months Ended
Dec. 01, 2017
Dec. 01, 2016
Dec. 01, 2015
Dec. 01, 2014
Nov. 30, 2017
Nov. 30, 2016
Nov. 30, 2015
Nov. 30, 2014
Dec. 31, 2017
Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Potential effect of restricted shares and share units, and performance shares excluded from diluted earnings per share computation                 1,700,000  
Impact of restricted shares, restricted share units and performance share units (in shares)                 0 1,400,000
Share-based compensation expense                 $ 5 $ 3
Potential effect of shares excluded from diluted earnings calculation (in shares)                 1,000,000  
Convertible Notes | 7.875% Convertible Notes Due 2026                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Interest rate                 7.875%  
Executive Officer                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Number or shares issuable per performance share unit (in shares)           1 1 1    
Executive Officer | Performance Shares                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Exercise price (in usd per share) $ 24.79 $ 12.77 $ 10.51 $ 13.74            
Executive Officer | Performance Shares | Performance period of October 1, 2017 to September 30, 2020                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance period         3 years          
Shares authorized for grant (in shares)         300,000          
Executive Officer | Performance Shares | Performance period of October 1, 2017 to September 30, 2020 | Minimum                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance-based vesting percentage                 0.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2017 to September 30, 2020 | Maximum                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance-based vesting percentage                 200.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2017 to September 30, 2020 | Performance Objective One                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Award vesting rights percentage                 50.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2017 to September 30, 2020 | Performance Objective Two                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Award vesting rights percentage                 50.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2016 to September 30, 2019                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance period           3 years        
Shares authorized for grant (in shares)           600,000        
Executive Officer | Performance Shares | Performance period of October 1, 2016 to September 30, 2019 | Minimum                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance-based vesting percentage                 0.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2016 to September 30, 2019 | Maximum                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance-based vesting percentage                 200.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2016 to September 30, 2019 | Performance Objective One                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Award vesting rights percentage                 50.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2016 to September 30, 2019 | Performance Objective Two                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Award vesting rights percentage                 25.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2016 to September 30, 2019 | Performance Objective Three                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Award vesting rights percentage                 25.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2015 to September 30, 2018                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance period             3 years      
Shares authorized for grant (in shares)             700,000      
Executive Officer | Performance Shares | Performance period of October 1, 2015 to September 30, 2018 | Minimum                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance-based vesting percentage                 0.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2015 to September 30, 2018 | Maximum                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance-based vesting percentage                 200.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2015 to September 30, 2018 | Performance Objective One                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Award vesting rights percentage                 50.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2015 to September 30, 2018 | Performance Objective Two                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Award vesting rights percentage                 50.00%  
Executive Officer | Performance Shares | Performance period of October 1, 2014 to September 30, 2017                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Performance period                 3 years  
Payout of performance share units 65.00%                  
Executive Officer | Restricted Share Units (RSUs)                    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                    
Exercise price (in usd per share)   $ 12.77 $ 10.51 $ 13.74            
Shares granted (in shares)         300,000 500,000 500,000 400,000    
Vesting period 3 years 3 years 3 years 3 years