Investments - Cost (amortized cost for fixed maturities and short-term investments), fair value, gross unrealized gains, gross unrealized (losses), and OTTI recorded in AOCI (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
AFS securities
Cost or amortized cost of Fixed maturities	$ 26,485,164		$ 27,111,874
Gross unrealized gains on Fixed maturities	943,348		807,684
Gross unrealized losses on Fixed maturities	(288,688)		(419,422)
Fixed maturities, at fair value	27,139,824		27,500,136
Gross Unrealized Losses Non-credit related OTTI	(83,472)	[1]	(86,882)	[1]
Short-term investments, amortized cost	382,509		455,470
Short-term investments, gross unrealized gains	181	[2]	962	[3]
Short-term investments, gross unrealized losses	(577)	[2]	(144)	[3]
Short-term investments, at fair value	382,113		456,288
Cost of equity securities	907,952		903,201
Equity securities, gross unrealized gains	166,197	[4]	154,506	[5]
Equity securities, gross unrealized losses	(18,756)	[4]	(17,470)	[5]
Equity securities, at fair value	1,055,393		1,040,237
Available for sale securities, Cost or amortized cost	27,775,625		28,470,545
Available for sale securities, Gross unrealized gains	1,109,726		963,152
Available for sale securities, Gross unrealized losses	308,021		437,036
Total investments available for sale	28,577,330		28,996,661
Fixed maturities - HTM
Fixed maturities, held to maturity	2,854,487		2,858,695
Fixed maturites held to maturity, gross unrealized gains	354,878		274,150
Fixed maturites held to maturity, gross unrealized losses	(190)		(1,610)
Fair value of held to maturity securities	3,209,175		3,131,235
U.S. Government and Government - Related/Supported
AFS securities
Cost or amortized cost of Fixed maturities	2,282,321		2,484,193
Gross unrealized gains on Fixed maturities	59,678	[2]	51,701	[3]
Gross unrealized losses on Fixed maturities	(22,947)	[2]	(34,043)	[3]
Fixed maturities, at fair value	2,319,052	[2]	2,501,851
Gross Unrealized Losses Non-credit related OTTI	0	[1],[2]	0	[1],[3]
Fixed maturities - HTM
Fixed maturities, held to maturity	11,052	[2]	10,993
Fixed maturites held to maturity, gross unrealized gains	918	[2]	629	[3]
Fixed maturites held to maturity, gross unrealized losses	0	[2]	0	[3]
Fair value of held to maturity securities	11,970		11,622
Corporate
AFS securities
Cost or amortized cost of Fixed maturities	10,697,760		10,802,332
Gross unrealized gains on Fixed maturities	490,229	[6],[7]	433,097	[8],[9]
Gross unrealized losses on Fixed maturities	(79,484)	[6],[7]	(109,599)	[8],[9]
Fixed maturities, at fair value	11,108,505		11,125,830
Gross Unrealized Losses Non-credit related OTTI	(4,758)	[1],[6],[7]	(4,758)	[1],[8],[9]
Fixed maturities - HTM
Fixed maturities, held to maturity	1,376,931		1,386,863
Fixed maturites held to maturity, gross unrealized gains	135,909		113,179
Fixed maturites held to maturity, gross unrealized losses	(190)		(968)
Fair value of held to maturity securities	1,512,650		1,499,074
RMBS - Agency
AFS securities
Cost or amortized cost of Fixed maturities	3,186,504		3,540,101
Gross unrealized gains on Fixed maturities	74,788		68,098
Gross unrealized losses on Fixed maturities	(38,809)		(62,077)
Fixed maturities, at fair value	3,222,483		3,546,122
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
RMBS - Non-Agency
AFS securities
Cost or amortized cost of Fixed maturities	389,181		396,798
Gross unrealized gains on Fixed maturities	36,836		33,096
Gross unrealized losses on Fixed maturities	(24,624)		(31,126)
Fixed maturities, at fair value	401,393		398,768
Gross Unrealized Losses Non-credit related OTTI	(71,999)	[1]	(74,528)	[1]
Fixed maturities - HTM
Fixed maturities, held to maturity	67,037		66,987
Fixed maturites held to maturity, gross unrealized gains	6,743		4,985
Fixed maturites held to maturity, gross unrealized losses	0		0
Fair value of held to maturity securities	73,780		71,972
CMBS
AFS securities
Cost or amortized cost of Fixed maturities	1,172,597		1,223,313
Gross unrealized gains on Fixed maturities	36,282		39,255
Gross unrealized losses on Fixed maturities	(10,567)		(15,773)
Fixed maturities, at fair value	1,198,312		1,246,795
Gross Unrealized Losses Non-credit related OTTI	(2,662)	[1]	(2,753)	[1]
Fixed maturities - HTM
Fixed maturities, held to maturity	145,005		144,924
Fixed maturites held to maturity, gross unrealized gains	15,215		11,864
Fixed maturites held to maturity, gross unrealized losses	0		0
Fair value of held to maturity securities	160,220		156,788
CDO
AFS securities
Cost or amortized cost of Fixed maturities	758,469		754,414
Gross unrealized gains on Fixed maturities	3,649		5,833
Gross unrealized losses on Fixed maturities	(37,058)		(42,934)
Fixed maturities, at fair value	725,060		717,313
Gross Unrealized Losses Non-credit related OTTI	(1,936)	[1]	(2,036)	[1]
Other asset-backed securities
AFS securities
Cost or amortized cost of Fixed maturities	1,156,561		1,210,384
Gross unrealized gains on Fixed maturities	46,219	[10]	40,560	[11]
Gross unrealized losses on Fixed maturities	(6,468)	[10]	(8,840)	[11]
Fixed maturities, at fair value	1,196,312		1,242,104
Gross Unrealized Losses Non-credit related OTTI	(2,117)	[1],[10]	(2,807)	[1],[11]
Fixed maturities - HTM
Fixed maturities, held to maturity	106,514		106,540
Fixed maturites held to maturity, gross unrealized gains	9,437	[10]	6,908	[11]
Fixed maturites held to maturity, gross unrealized losses	0	[10]	0	[11]
Fair value of held to maturity securities	115,951		113,448
U.S. States and political subdivisions of the States
AFS securities
Cost or amortized cost of Fixed maturities	1,832,247		1,821,499
Gross unrealized gains on Fixed maturities	84,695		55,083
Gross unrealized losses on Fixed maturities	(14,491)		(30,770)
Fixed maturities, at fair value	1,902,451		1,845,812
Gross Unrealized Losses Non-credit related OTTI	0	[1]	0	[1]
Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported
AFS securities
Cost or amortized cost of Fixed maturities	5,009,524		4,878,840
Gross unrealized gains on Fixed maturities	110,972	[2]	80,961	[3]
Gross unrealized losses on Fixed maturities	(54,240)	[2]	(84,260)	[3]
Fixed maturities, at fair value	5,066,256	[2]	4,875,541
Gross Unrealized Losses Non-credit related OTTI	0	[1],[2]	0	[1],[3]
Fixed maturities - HTM
Fixed maturities, held to maturity	1,147,948	[2]	1,142,388
Fixed maturites held to maturity, gross unrealized gains	186,656	[2]	136,585	[3]
Fixed maturites held to maturity, gross unrealized losses	0	[2]	(642)	[3]
Fair value of held to maturity securities	$ 1,334,604		$ 1,278,331

[1] Represents the non-credit component of OTTI losses, adjusted for subsequent sales of securities. It does not include the change in fair value subsequent to the impairment measurement date.

[2] U.S. Government and Government-Related/Supported, Non-U.S. Sovereign Government, Provincials, Supranationals and Government-Related/Supported and Total short-term investments includes government-related securities with an amortized cost of $2,301.8 million and fair value of $2,365.0 million and U.S. Agencies with an amortized cost of $238.0 million and fair value of $261.5 million.

[3] U.S. Government and Government-Related/Supported, Non-U.S. Sovereign Government, Provincials, Supranationals and Government-Related/Supported and Total short-term investments includes government-related securities with an amortized cost of $2,241.5 million and fair value of $2,275.6 million and U.S. Agencies with an amortized cost of $267.0 million and fair value of $284.3 million.

[4] Included within Total equity securities are investments in fixed income funds with a fair value of $89.1 million and an amortized cost of $100.9 million.

[5] Included within Total equity securities are investments in fixed income funds with a fair value of $87.4 million and an amortized cost of $100.0 million.

[6] Included within Corporate are Tier One and Upper Tier Two securities, representing committed term debt and hybrid instruments, which are senior to the common and preferred equities of the financial institutions. These securities have a fair value of $279.8 million and an amortized cost of $281.3 million.

[7] Included within Corporate are certain medium term notes supported primarily by pools of European investment grade credit with varying degrees of leverage. The notes have a fair value of $154.7 million and an amortized cost of $146.2 million. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.

[8] Included within Corporate are Tier One and Upper Tier Two securities, representing committed term debt and hybrid instruments, which are senior to the common and preferred equities of the financial institutions. These securities have a fair value of $282.2 million and an amortized cost of $286.2 million.

[9] Included within Corporate are certain medium term notes supported primarily by pools of European investment grade credit with varying degrees of leverage. The notes have a fair value of $154.6 million and an amortized cost of $147.7 million. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.

[10] Covered Bonds within Fixed maturities - AFS with an amortized cost of $508.3 million and a fair value of $537.5 million and Covered Bonds within Fixed maturities - HTM with an amortized cost of $8.6 million and a fair value of $8.9 million are included within Other asset-backed securities to align the Company's classification to market indices.

[11] Covered Bonds within Fixed maturities - AFS with an amortized cost of $526.4 million and a fair value of $553.1 million and Covered Bonds within Fixed maturities - HTM with an amortized cost of $8.6 million and a fair value of $8.7 million are included within Other asset-backed securities to align the Company's classification to market indices.