Investments - Equity Securities At Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Equity securities, at fair value	$ 22,163	$ 21,430
Public Equity [Member]
Percentage of investment in equity securities	11.00%	7.00%
Private Equity [Member]
Percentage of investment in equity securities	89.00%	93.00%
Public And Private Equity [Member]
Percentage of investment in equity securities	100.00%	100.00%
Corporate [Member]
Percentage of investment in equity securities	79.00%	81.00%
Real Estate [Member]
Percentage of investment in equity securities	21.00%	19.00%
Corporate And Real Estate [Member]
Percentage of investment in equity securities	100.00%	100.00%
Americas [Member]
Percentage of investment in equity securities	50.00%	53.00%
Europe Middle East And Africa [Member]
Percentage of investment in equity securities	17.00%	16.00%
Asia [Member]
Percentage of investment in equity securities	33.00%	31.00%
Americas Europe And Asia [Member]
Percentage of investment in equity securities	100.00%	100.00%