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Schedule I - Summary Of Investments - Other Than Investments In Related Parties (Detail)
$ in Millions
Dec. 31, 2022
USD ($)
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost $ 9,968
Market value 8,997
Amount at which shown in the balance sheet 8,998
Short-term Investments  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 63
Market value 62
Amount at which shown in the balance sheet 63
U.S. Treasury bonds  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 309
Market value 303
Amount at which shown in the balance sheet 303
Municipal bonds  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 1,671
Market value 1,479
Amount at which shown in the balance sheet 1,479
Foreign government bonds  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 208
Market value 194
Amount at which shown in the balance sheet 194
Governmental agency bonds  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 248
Market value 229
Amount at which shown in the balance sheet 229
Governmental agency mortgage-backed securities  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 5,253
Market value 4,601
Amount at which shown in the balance sheet 4,601
U.S. corporate debt securities  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 1,004
Market value 921
Amount at which shown in the balance sheet 921
Foreign corporate debt securities  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 477
Market value 443
Amount at which shown in the balance sheet 443
Debt Securities  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 9,170
Market value 8,170
Amount at which shown in the balance sheet 8,170
Equity Securities, Investment Summary  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 724
Market value 754 [1]
Amount at which shown in the balance sheet 754
Notes Receivable  
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]  
Cost 11
Market value 11
Amount at which shown in the balance sheet $ 11
[1] Included in equity securities are non-marketable equity securities and equity method investments. Estimates of fair value for these investments could not be made without incurring excessive costs.