Fair Value Measurements - Narrative (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	$ 27,139,824	$ 27,500,136
Amortized cost of fixed maturities	26,485,164	27,111,874
Equity securities, at fair value	1,055,393	1,040,237
Other investments - structured transactions	288,047	294,048
Spread on U.S. treasury for discounting deposit liabilities	0.548%	0.567%
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	11,108,505	11,125,830
Amortized cost of fixed maturities	10,697,760	10,802,332
Medium term notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	154,700	154,600
Amortized cost of fixed maturities	146,200	147,700
Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	1,196,312	1,242,104
Amortized cost of fixed maturities	1,156,561	1,210,384
Covered bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, at fair value	537,500	553,100
Amortized cost of fixed maturities	508,300	526,400
Fixed income funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, at fair value	$ 89,100	$ 87,400