Investments - Debt Securities At Fair Value (Detail) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Debt securities, at fair value | $ 16,981 | $ 16,570 |
| Corporate debt securities [Member] | ||
| Debt securities, at fair value | 10,991 | 10,838 |
| Securities backed by real estate [Member] | ||
| Debt securities, at fair value | 1,940 | 2,619 |
| Money Market Instruments [Member] | ||
| Debt securities, at fair value | 2,185 | 1,681 |
| Other [Member] | ||
| Debt securities, at fair value | $ 1,865 | $ 1,432 |