Fair Value Measurements - Guaranteed Minimum Income Benefit Contracts (Details) (Variable Annuity [Member], Guaranteed Minimum Income Benefit [Member])	3 Months Ended
	Mar. 31, 2013
Maximum [Member] | Guaranteed Minimum Income Benefits Assets [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Nonperformance risk adjustment	90
Maximum [Member] | GMIB Liabilities [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Nonperformance risk adjustment	130
Minimum [Member] | Guaranteed Minimum Income Benefits Assets [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Nonperformance risk adjustment	0
Minimum [Member] | GMIB Liabilities [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Nonperformance risk adjustment	5
Weighted Average [Member] | Guaranteed Minimum Income Benefits Assets [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Nonperformance risk adjustment	30
Weighted Average [Member] | GMIB Liabilities [Member]
Long-Duration Contracts, Assumptions by Product and Guarantee [Line Items]
Nonperformance risk adjustment	55