Investments - Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Cost or Amortized Cost, Due in one year or less	$ 1,779	$ 1,574
Cost or Amortized Cost, Due after one year through five years	7,566	7,738
Cost or Amortized Cost, Due after five years through ten years	15,892	14,652
Cost or Amortized Cost, Due after ten years	13,112	13,303
Cost or Amortized Cost, Total	38,349	37,267
Estimated Fair Value, Due in one year or less	1,828	1,595
Estimated Fair Value, Due after one year through five years	7,955	8,082
Estimated Fair Value, Due after five years through ten years	16,332	14,915
Estimated Fair Value, Due after ten years	14,778	14,989
Estimated Fair Value, Total	$ 40,893	$ 39,581