Total Investments in the Bank and Financial Institution Sector, Including those Classified as Perpetual Securities (Detail) (Banks/financial Institutions, USD $) In Millions, unless otherwise specified	Sep. 30, 2011	Dec. 31, 2010
Summary of Investment Holdings [Line Items]
Amortized Cost	$ 27,770	$ 29,540
Fair value	25,333	27,910
Percentage of Total Investment Portfolio, Amortized Cost	28.00%	35.00%
Percentage of Total Investment Portfolio, Fair Value	26.00%	32.00%
Perpetual Securities | Upper Tier II
Summary of Investment Holdings [Line Items]
Amortized Cost	4,637	4,957
Fair value	4,222	4,748
Percentage of Total Investment Portfolio, Amortized Cost	5.00%	6.00%
Percentage of Total Investment Portfolio, Fair Value	4.00%	5.00%
Perpetual Securities | Tier I
Summary of Investment Holdings [Line Items]
Amortized Cost	2,518	2,542
Fair value	1,991	2,421
Percentage of Total Investment Portfolio, Amortized Cost	2.00%	3.00%
Percentage of Total Investment Portfolio, Fair Value	2.00%	3.00%
Debt Securities
Summary of Investment Holdings [Line Items]
Amortized Cost	20,615	22,041
Fair value	$ 19,120	$ 20,741
Percentage of Total Investment Portfolio, Amortized Cost	21.00%	26.00%
Percentage of Total Investment Portfolio, Fair Value	20.00%	24.00%