Investments - Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Cost or Amortized Cost, Due in one year or less	$ 1,574	$ 2,479
Cost or Amortized Cost, Due after one year through five years	7,738	9,070
Cost or Amortized Cost, Due after five years through ten years	14,652	12,055
Cost or Amortized Cost, Due after ten years	13,303	13,728
Cost or Amortized Cost, Total	37,267	37,332
Estimated Fair Value, Due in one year or less	1,595	2,511
Estimated Fair Value, Due after one year through five years	8,082	9,621
Estimated Fair Value, Due after five years through ten years	14,915	12,584
Estimated Fair Value, Due after ten years	14,989	16,049
Estimated Fair Value, Total	$ 39,581	$ 40,765