Investment Exposure to Sovereign Debt and Financial Institutions (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011		Dec. 31, 2010
PIIGS | Sovereign and Supranational
Summary of Investment Holdings [Line Items]
Amortized Cost	$ 1,102		$ 1,037
Fair value	1,095		1,088
PIIGS | Sovereign and Supranational | Italy
Summary of Investment Holdings [Line Items]
Amortized Cost	326		307
Fair value	313		306
PIIGS | Sovereign and Supranational | Spain
Summary of Investment Holdings [Line Items]
Amortized Cost	776		730
Fair value	782		782
PIIGS | Banks/financial Institutions
Summary of Investment Holdings [Line Items]
Amortized Cost	1,301	[1]	3,431	[1]
Fair value	983		2,506
Percentage of Total Investments in Banks and Financial Sector, Amortized Cost	5.00%		12.00%
Percentage of Total Investment Portfolio, Amortized Cost	1.00%		4.00%
PIIGS | Banks/financial Institutions | Italy
Summary of Investment Holdings [Line Items]
Amortized Cost	196		184
Fair value	187		183
PIIGS | Banks/financial Institutions | Ireland
Summary of Investment Holdings [Line Items]
Amortized Cost	552		710
Fair value	330		659
PIIGS | Banks/financial Institutions | Greece
Summary of Investment Holdings [Line Items]
Amortized Cost	0		1,152
Fair value	0		391
PIIGS | Banks/financial Institutions | Portugal
Summary of Investment Holdings [Line Items]
Amortized Cost	0		859
Fair value	0		770
PIIGS | Banks/financial Institutions | Spain
Summary of Investment Holdings [Line Items]
Amortized Cost	553		526
Fair value	466		503
Banks/financial Institutions
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%

[1] Represents 5% in 2011 and 12% in 2010 of total investments in the banks and financial institutions sector, and 1% in 2011 and 4% in 2010 of total investments in debt and perpetual securities