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Leases (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Leases [Abstract]      
Rental expense for operating leases $ 16 $ 17 $ 16
Minimum payments for operating leases having initial or remaining non-cancelable terms      
2018 8    
2019 6    
2020 4    
2021 3    
2022 3    
Thereafter 3    
Total 27    
Commitment to purchase corporate headquarters building $ 91