Investments - Equity Securities At Fair Value (Detail) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Equity securities, at fair value | $ 19,781 | $ 22,163 |
| Public Equity [Member] | ||
| Percentage of investment in equity securities | 15.00% | 11.00% |
| Private Equity [Member] | ||
| Percentage of investment in equity securities | 85.00% | 89.00% |
| Public And Private Equity [Member] | ||
| Percentage of investment in equity securities | 100.00% | 100.00% |
| Corporate [Member] | ||
| Percentage of investment in equity securities | 83.00% | 79.00% |
| Real Estate [Member] | ||
| Percentage of investment in equity securities | 17.00% | 21.00% |
| Corporate And Real Estate [Member] | ||
| Percentage of investment in equity securities | 100.00% | 100.00% |