Reinsurance - Guaranteed Minimum Death Benefits Account Value, Net Amount at Risk and Contractholders (Details) (Variable Annuity [Member], Guaranteed Minimum Death Benefit [Member], USD $)
In Billions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2015
Contractholders
Dec. 31, 2014
Contractholders
Variable Annuity [Member] | Guaranteed Minimum Death Benefit [Member]
   
Guaranteed Minimum Death Benefits Account Value, Net Amount at Risk And Average Age Table [Line Items]    
Account value $ 12.9 $ 13.1
Net amount at risk $ 2.7 $ 2.8
Number of contractholders 346,000 354,000