Investments - Equity Securities At Fair Value (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Equity securities, at fair value	$ 21,221	$ 22,163
Public Equity [Member]
Percentage of investment in equity securities	10.00%	11.00%
Private Equity [Member]
Percentage of investment in equity securities	90.00%	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	77.00%	79.00%
Real Estate [Member]
Percentage of investment in equity securities	23.00%	21.00%
Corporate And Real Estate [Member]
Percentage of investment in equity securities	100.00%	100.00%
Americas [Member]
Percentage of investment in equity securities	46.00%	50.00%
Europe Middle East And Africa [Member]
Percentage of investment in equity securities	19.00%	17.00%
Asia [Member]
Percentage of investment in equity securities	35.00%	33.00%
Americas Europe And Asia [Member]
Percentage of investment in equity securities	100.00%	100.00%