Fair Value Measurements - Guaranteed Minimum Income Benefit Contracts Assets (Details) (Derivative Financial Instruments, Assets [Member], Variable Annuity [Member], Guaranteed Minimum Income Benefit [Member])	9 Months Ended
	Sep. 30, 2013
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Nonperformance risk adjustment, counterparty	0.85%
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Nonperformance risk adjustment, counterparty	0.00%
Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Nonperformance risk adjustment, counterparty	0.15%