Fair Value (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 32,400	$ 25,427
Debt Securities, Available-for-sale	46,263	44,895
Equity Securities, FV-NI	1,923	2,553
Assets under management	0	3,755
Assets, Fair Value Disclosure	80,586	76,630
Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	46,263	44,895
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	4,828	4,443
State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	7,068	7,353
Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	23,053	22,017
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	8,630	8,296
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	2,684	2,786
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	32,230	25,345
Equity Securities, FV-NI	1,833	2,468
Assets under management		1,505
Assets, Fair Value Disclosure	38,772	33,500
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	4,709	4,182
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	4,682	4,167
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	27	15
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	170	82
Equity Securities, FV-NI	25	16
Assets under management		2,140
Assets, Fair Value Disclosure	41,442	42,749
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	41,247	40,511
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	146	276
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	7,068	7,353
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	22,719	21,800
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	8,630	8,296
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	2,684	2,786
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	65	69
Assets under management		110
Assets, Fair Value Disclosure	372	381
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	307	202
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	307	202
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