Fair Value Measurements - Narrative (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	$ 30,442,921	$ 27,500,136
Amortized cost of fixed maturities	29,065,531	27,111,874
Equity securities, at fair value	988,710	1,040,237
Other investments - structured transactions	275,821	294,048
Spread on U.S. treasury for discounting deposit liabilities	0.455%	0.567%
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value		11,125,830
Amortized cost of fixed maturities		10,802,332
Medium term notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	155,900	154,600
Amortized cost of fixed maturities	143,600	147,700
Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value		1,242,104
Amortized cost of fixed maturities		1,210,384
Covered bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	763,600	553,100
Amortized cost of fixed maturities	737,000	526,400
Fixed income funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, at fair value	$ 92,100	$ 87,400