Reinsurance - Guaranteed Minimum Death Benefits Account Value, 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, 2013 Contractholders	Dec. 31, 2012 Contractholders
Variable Annuity [Member] | Guaranteed Minimum Death Benefit [Member]
Guaranteed Minimum Death Benefits Account Value Risk And Average Age Table [Line Items]
Account value	$ 13.7	$ 13.3
Net amount at risk	$ 3.6	$ 4.0
Guaranteed Minimum Death Benefits Total Contractholders	425,000	435,000