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Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | $ 16,524 | $ 6,065
Gross Unrealized Losses | 1,157 | 112
U.S. Government, Government agencies and Government-sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 2,095 | 898
Gross Unrealized Losses | 116 | 8
AAA |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 993 | 368
Gross Unrealized Losses | 105 | 6
AA |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 2,809 | 875
Gross Unrealized Losses | 269 | 17
A |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 3,300 | 1,516
Gross Unrealized Losses | 205 | 23
BBB |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 6,073 | 1,812
Gross Unrealized Losses | 392 | 42
Non-investment grade |  |
Debt Securities, Available-for-sale [Line Items] |  |
Estimated Fair Value | 1,254 | 596
Gross Unrealized Losses | $ 70 | $ 16

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