Investments - Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Cost or Amortized Cost, Due in one year or less	$ 1,334	$ 1,350
Cost or Amortized Cost, Due after one year through five years	9,746	7,979
Cost or Amortized Cost, Due after five years through ten years	14,892	16,859
Cost or Amortized Cost, Due after ten years	12,134	11,893
Cost or Amortized Cost, Total	38,106	38,081
Estimated Fair Value, Due in one year or less	1,356	1,359
Estimated Fair Value, Due after one year through five years	10,186	8,139
Estimated Fair Value, Due after five years through ten years	15,931	16,870
Estimated Fair Value, Due after ten years	14,714	13,174
Estimated Fair Value, Total	$ 42,187	$ 39,542