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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
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Expense Related to Revaluation of Federal Benefit - TCJA | $ 14 |  |
Reduced Expense Related to Revaluation of Federal Benefits - TCJA | 4 |  |
Allowance for Bad Debts |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Jan. 1 | 52 | $ 51 | $ 52
Charged to costs and expenses | 42 | 39 | 39
Charged to other accounts | 11 | 10 | 11
Deductions from reserves | (50) | (48) | (51)
Balance at Dec. 31 | 55 | 52 | 51
NOL and Tax Credit Valuation Allowances |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Jan. 1 | 77 | 58 | 28
Charged to costs and expenses | 7 | 9 | 3
Charged to other accounts | 0 | 22 | 35
Deductions from reserves | (5) | (12) | (8)
Balance at Dec. 31 | $ 79 | $ 77 | $ 58

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