Investments - Schedule of Fixed Maturities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Amortized Cost, net
Due in one year or less	$ 98,115
Due after one year through five years	900,326
Due after five years through ten years	1,757,273
Due after ten years through twenty years	6,862,449
Due after twenty years	8,045,149
Mortgage-backed and asset-backed securities	141,610
Fixed maturities, net of allowance for credit losses	17,804,922
Fair Value
Due in one year or less	99,760
Due after one year through five years	995,569
Due after five years through ten years	2,083,816
Due after ten years through twenty years	8,653,145
Due after twenty years	9,301,053
Mortgage-backed and asset-backed securities	171,944
Fixed maturities, fair value	$ 21,305,287	$ 21,213,509