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Income Taxes - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]      
Income tax expense (benefit) from change in tax rate $ 54    
Operating Loss Carryforwards [Line Items]      
Income tax expense (benefit) (100) $ 153 $ 179
Excess tax benefits from share-based compensation   2 8
Deferred tax assets 41    
Increase in deferred tax asset valuation allowance 25    
Valuation allowance 41 16  
Impact on effective tax rate if tax benefits are recognized 12 $ 9 $ 7
Liability for unrecognized tax benefits, potential decrease 2    
State      
Operating Loss Carryforwards [Line Items]      
Net operating loss carryforwards 578    
Tax credit carryovers 14    
Federal      
Operating Loss Carryforwards [Line Items]      
Tax credit carryovers $ 4