Investments - Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Cost or Amortized Cost, Due in one year or less	$ 1,817	$ 1,574
Cost or Amortized Cost, Due after one year through five years	8,616	7,738
Cost or Amortized Cost, Due after five years through ten years	14,583	14,652
Cost or Amortized Cost, Due after ten years	12,812	13,303
Cost or Amortized Cost, Total	37,828	37,267
Estimated Fair Value, Due in one year or less	1,855	1,595
Estimated Fair Value, Due after one year through five years	9,114	8,082
Estimated Fair Value, Due after five years through ten years	15,466	14,915
Estimated Fair Value, Due after ten years	15,412	14,989
Estimated Fair Value, Total	$ 41,847	$ 39,581