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Valuation and Qualifying Accounts (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Valuation account for accounts receivable:      
Valuation Account      
Balance at Beginning of Period $ 2 $ 3 $ 3
Charged to Costs and Expenses (1) 0 1
Charged to Other Accounts 0 0 0
Deductions  0 1 1
Balance at End of Period 1 2 3
Valuation account for deferred tax assets:      
Valuation Account      
Balance at Beginning of Period 421 56 134
Charged to Costs and Expenses 1 6 0
Charged to Other Accounts 3 375 0
Deductions  12 16 78
Balance at End of Period $ 413 $ 421 $ 56