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Investments - Summary of Net Investment Income (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Investment [Line Items] |  |  |
Net Realized and Unrealized Gain (Loss) on Trading Securities | $ 23 | $ 0 | $ 24
Trading Securities, Realized Gain (Loss) | 1 | (18) | 7
Fixed income securities |  | 103 | 183
Investment expense | (6) | (6) | (6)
Securities available-for-sale and short-term | 74 | 103 | 196
Net investment income | 139 | 122 | 227
Gains (losses) on securities held as of reporting date [Member] |  |  |
Investment [Line Items] |  |  |
Other Investments Income | 22 | 18 | 17
Available-for-sale Securities [Member] |  |  |
Investment [Line Items] |  |  |
Fixed income securities | 78 |  |
Short-term Investments [Member] |  |  |
Investment [Line Items] |  |  |
Fixed income securities | 0 | 5 | 17
Financing Receivable [Member] |  |  |
Investment [Line Items] |  |  |
Fixed income securities | 0 | 1 | 1
Other Investments [Member] |  |  |
Investment [Line Items] |  |  |
Fixed income securities | $ 66 | $ 19 | $ 32

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