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Fair Value (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents $ 27,210 $ 25,312
Debt Securities, Available-for-sale 46,822 46,919
Equity Securities, FV-NI 2,444 1,948
Assets, Fair Value Disclosure 76,476 74,179
Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 46,822 46,919
U.S. Government and Agency Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 3,728 4,327
State and Municipal Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 6,494 6,984
Corporate Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 24,309 23,307
U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 9,632 9,584
Non-U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 2,659 2,717
Quoted Prices in Active Markets (Level 1) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 21,305 25,248
Equity Securities, FV-NI 2,023 1,859
Assets, Fair Value Disclosure 26,889 31,330
Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 3,561 4,223
Quoted Prices in Active Markets (Level 1) [Member] | U.S. Government and Agency Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 3,561 4,194
Quoted Prices in Active Markets (Level 1) [Member] | State and Municipal Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 0 0
Quoted Prices in Active Markets (Level 1) [Member] | Corporate Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 0 29
Quoted Prices in Active Markets (Level 1) [Member] | U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 0 0
Quoted Prices in Active Markets (Level 1) [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 0 0
Other Observable Inputs (Level 2) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 5,905 64
Equity Securities, FV-NI 214 24
Assets, Fair Value Disclosure 48,913 42,347
Other Observable Inputs (Level 2) [Member] | Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 42,794 42,259
Other Observable Inputs (Level 2) [Member] | U.S. Government and Agency Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 167 133
Other Observable Inputs (Level 2) [Member] | State and Municipal Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 6,494 6,984
Other Observable Inputs (Level 2) [Member] | Corporate Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 23,842 22,841
Other Observable Inputs (Level 2) [Member] | U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 9,632 9,584
Other Observable Inputs (Level 2) [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 2,659 2,717
Unobservable Inputs (Level 3) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0 0
Equity Securities, FV-NI 207 65
Assets, Fair Value Disclosure 674 502
Unobservable Inputs (Level 3) [Member] | Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 467 437
Unobservable Inputs (Level 3) [Member] | U.S. Government and Agency Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 0 0
Unobservable Inputs (Level 3) [Member] | State and Municipal Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 0 0
Unobservable Inputs (Level 3) [Member] | Corporate Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 467 437
Unobservable Inputs (Level 3) [Member] | U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale 0 0
Unobservable Inputs (Level 3) [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Available-for-sale $ 0 $ 0