Investments - Available-For-Sale Fixed Maturity Securities by Contractual Maturity (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Cost or Amortized Cost, Due in one year or less	$ 1,783	$ 1,648
Cost or Amortized Cost, Due after one year through five years	12,916	13,603
Cost or Amortized Cost, Due after five years through ten years	9,430	8,726
Cost or Amortized Cost, Due after ten years	14,341	14,164
Cost or Amortized Cost, Total	38,470	38,141
Estimated Fair Value, Due in one year or less	1,819	1,665
Estimated Fair Value, Due after one year through five years	13,731	14,442
Estimated Fair Value, Due after five years through ten years	10,267	9,555
Estimated Fair Value, Due after ten years	16,919	16,942
Estimated Fair Value, Total	$ 42,736	$ 42,604