Investments - Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Cost or Amortized Cost, Due in one year or less	$ 2,011	$ 2,479
Cost or Amortized Cost, Due after one year through five years	8,776	9,070
Cost or Amortized Cost, Due after five years through ten years	12,401	12,055
Cost or Amortized Cost, Due after ten years	13,667	13,728
Cost or Amortized Cost, Total	36,855	37,332
Estimated Fair Value, Due in one year or less	2,043	2,511
Estimated Fair Value, Due after one year through five years	9,354	9,621
Estimated Fair Value, Due after five years through ten years	13,108	12,584
Estimated Fair Value, Due after ten years	16,078	16,049
Estimated Fair Value, Total	$ 40,583	$ 40,765