Investments (Held-To-Maturity Securities Continuous Unrealized Loss Position) (Detail) (Variable Interest Entity [Member], Mortgage And Other Asset-Backed Securities [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Variable Interest Entity [Member] | Mortgage And Other Asset-Backed Securities [Member]
Variable Interest Entity [Line Items]
Less than 12 Months, Fair Value		$ 284
Less than 12 Months, Unrealized Losses		(31)
12 Months or Longer, Fair Value	2,350	2,185
12 Months or Longer, Unrealized Losses	(168)	(340)
Total, Fair Value	2,350	2,469
Total, Unrealized Loss	$ (168)	$ (371)