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Valuation and Qualifying Accounts (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Current Portion of Casualty and Other Claims Included in Accounts Payable      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Beginning Balance $ 212 $ 213 $ 187
Expenses 27 22 32
Other Accounts [1] 81 131 145
Deductions [2] 138 154 151
Ending Balance 182 212 213
Casualty and Other Claims Included in Other Liabilities      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Beginning Balance 171 158 179
Expenses [3] 80 89 85
Other Accounts 0 0 0
Deductions [4] 82 76 106
Ending Balance $ 169 $ 171 $ 158
[1] Includes revenue refunds and overcharges provided through deductions from operating revenues and transfers  from other accounts.
[2] Payments and reclassifications to/from accounts payable.
[3] Includes adjustments for changes in estimates for prior years’ claims.
[4] Payments and reclassifications to/from other liabilities.