INVESTMENTS - Composition of Investments in Unrealized Loss Position (Detail)	Jun. 30, 2013	Dec. 31, 2012
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	100.00%	100.00%
Percentage of Total Unrealized Losses	100.00%	100.00%
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	95.00%	96.00%
Percentage of Total Unrealized Losses	86.00%	89.00%
Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	5.00%	4.00%
Percentage of Total Unrealized Losses	14.00%	11.00%
Japan government and agencies | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	12.00%	43.00%
Percentage of Total Unrealized Losses	2.00%	9.00%
Public Utilities | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	16.00%	11.00%
Percentage of Total Unrealized Losses	13.00%	12.00%
Sovereign and Supranational | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	3.00%	3.00%
Percentage of Total Unrealized Losses	3.00%	6.00%
Banks/financial Institutions | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	19.00%	18.00%
Percentage of Total Unrealized Losses	27.00%	39.00%
Other Corporate | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of Total Investments in an Unrealized Loss Position	45.00%	21.00%
Percentage of Total Unrealized Losses	41.00%	23.00%
Investment Grade | Perpetual Securities
Investments, Unrealized Loss Position [Line Items]
Percentage of unrealized losses attributable to securities that were investment grade	87.00%	100.00%
Investment Grade | Japan government and agencies | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of unrealized losses attributable to securities that were investment grade	100.00%	100.00%
Investment Grade | Public Utilities | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of unrealized losses attributable to securities that were investment grade	87.00%	69.00%
Investment Grade | Sovereign and Supranational | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of unrealized losses attributable to securities that were investment grade	97.00%	96.00%
Investment Grade | Banks/financial Institutions | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of unrealized losses attributable to securities that were investment grade	72.00%	76.00%
Investment Grade | Other Corporate | Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Percentage of unrealized losses attributable to securities that were investment grade	94.00%	72.00%