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Income Taxes - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Operating Loss Carryforwards [Line Items]      
Operating loss carryforwards $ 332    
Change in tax rate, deferred tax asset, income tax expense (benefit)   $ 54  
Income tax (benefit) expense 292 (100) $ 153
Measurement period adjustment, income tax expense (benefit) 4    
Deferred tax assets 28    
Increase in deferred tax asset valuation allowance 13    
Valuation allowance 28 41  
Impact on effective tax rate if tax benefits are recognized 18 $ 12 $ 9
Liability for unrecognized tax benefits, potential decrease 3    
State      
Operating Loss Carryforwards [Line Items]      
Tax credit carryovers $ 14