Fair Value Measurements - Narrative (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, AFS, at fair value	$ 29,359,034	$ 27,500,136
Amortized cost of fixed maturities, available for sale	27,728,771	27,111,874
Spread on US Treasury rate for determining discount rate for fair value of deposit liabilities	29.50%	56.70%
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, AFS, at fair value		11,125,830
Amortized cost of fixed maturities, available for sale		10,802,332
Medium-term Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, AFS, at fair value	79,900	154,600
Amortized cost of fixed maturities, available for sale	68,400	147,700
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments - structured transactions	$ 354,382	$ 294,048