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Schedule V - Valuation And Qualifying Accounts (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Reserve Deducted From Accounts Receivable      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period $ 14 $ 13 $ 14
Additions Charged to costs and expenses 4 7 4
Deductions from reserve [1] 4 6 5
Balance at end of period 14 14 13
Reserve For Known And Incurred But Not Reported Claims      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 1,178 1,063 1,042
Additions Charged to costs and expenses 589 580 446
Additions Charged to other accounts (1) 6 (10)
Deductions from reserve [2] 482 471 415
Balance at end of period 1,284 1,178 1,063
Reserve Deducted From Deferred Income Taxes      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 9 10 11
Deductions from reserve 1 1 1
Balance at end of period $ 8 $ 9 $ 10
[1] Amount represents accounts written off, net of recoveries.
[2] Amount represents claim payments, net of recoveries.