Composition of Investments in Unrealized Loss Position in Bank and Financial Institution Sector (Detail) (Banks/financial Institutions)	Dec. 31, 2011	Dec. 31, 2010
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	46.00%	53.00%
Percentage of Total Unrealized Losses	62.00%	71.00%
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	37.00%	39.00%
Percentage of Total Unrealized Losses	44.00%	54.00%
Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	9.00%	14.00%
Percentage of Total Unrealized Losses	18.00%	17.00%
Perpetual Securities | Upper Tier II
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	4.00%	9.00%
Percentage of Total Unrealized Losses	6.00%	10.00%
Perpetual Securities | Tier I
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	5.00%	5.00%
Percentage of Total Unrealized Losses	12.00%	7.00%