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Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Allowances for Doubtful Accounts and Authorized Credits      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at beginning of period $ 0 $ 0 $ 1
Credited / charged to net income 2 1 1
Charges utilized / write-offs (1) (1) (2)
Balance at end of period 1 0 0
Tax Valuation Allowance      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at beginning of period 7 6 5
Credited / charged to net income 0 1 1
Charges utilized / write-offs 0 0 0
Balance at end of period $ 7 $ 7 $ 6