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Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | $ 28,266 | $ 29,511
Gross Unrealized Losses | 3,418 | 4,056
U.S. Government, Government agencies and Government-sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 2,357 | 2,355
Gross Unrealized Losses | 302 | 337
AAA |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 1,424 | 1,559
Gross Unrealized Losses | 260 | 298
AA |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 4,053 | 4,327
Gross Unrealized Losses | 670 | 817
A |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 6,440 | 6,615
Gross Unrealized Losses | 619 | 749
BBB |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 12,651 | 13,226
Gross Unrealized Losses | 1,360 | 1,621
Non-investment grade |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 1,341 | 1,429
Gross Unrealized Losses | $ 207 | $ 234

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