Investments (Details 8) (Alternative residential mortgage loans [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010
Alt-A RMBS by vintage year and certain other selected data
% of Total	100.00%	100.00%
Accumulated Other Comprehensive Income (Loss) Net Unrealized Investment Gains (Losses)
Alt-A RMBS by vintage year and certain other selected data
Amount	$ (680)	$ (670)
Rated Aa/AA or Better [Member]
Alt-A RMBS by vintage year and certain other selected data
% of Total	12.40%	15.90%
Rated NAIC 1 [Member]
Alt-A RMBS by vintage year and certain other selected data
% of Total	39.40%	39.50%
Fixed rate mortgage loans collateral [Member]
Alt-A RMBS by vintage year and certain other selected data
% of Total	92.30%	90.70%
Hybrid adjustable rate mortgage loans collateral [Member]
Alt-A RMBS by vintage year and certain other selected data
% of Total	7.70%	9.30%