Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	$ 33,276,322	$ 29,359,034
Amortized cost of fixed maturities	32,207,019	27,728,771
Other investments - structured transactions	$ 346,400	$ 354,400
Spread on U.S. treasury for discounting deposit liabilities	0.505%	0.295%
Medium term notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	$ 74,300	$ 79,900
Amortized cost of fixed maturities	$ 64,600	$ 68,400