SCHEDULE II - Condensed Statements of Cash Flows - Parent Company Only (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Cash flows from operating activities
Net income (loss)	$ 673,442,000		$ 1,134,514,000		$ (520,291,000)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Other, net	(108,525,000)		(52,246,000)		(8,647,000)
Net cash provided by operating activities	827,267,000		693,293,000		573,635,000
Payments/ proceeds from trading securities [Line Items]
Sales and redemptions of short-term investments	312,376,000		110,360,000		336,456,000
Purchases of short-term investments	(176,339,000)		(215,473,000)		(331,432,000)
Other, net	(786,000)		995,000		(186,823,000)
Net cash provided by (used in) investing activities	417,993,000		(219,538,000)		(1,080,378,000)
Cash flows from financing activities
Dividends paid to common and preferred shareholders	(200,078,000)		(217,615,000)		(205,784,000)
Repurchase of common shares	(715,421,000)		(504,991,000)		(413,737,000)
Issuance of common shares	51,111,000		34,323,000		16,041,000
Net proceeds from issuance of preferred shares	241,265,000		0		361,722,000
Redemption of preferred shares	(290,000,000)		0		0
Net cash used in financing activities	(865,930,000)		(688,283,000)		(241,758,000)
Effect of foreign exchange rate changes on cash	(4,550,000)		(6,024,000)		(20,326,000)
Decrease in cash and cash equivalents	374,780,000		(220,552,000)		(768,827,000)
Cash and cash equivalents - beginning of year	1,121,705,000		1,342,257,000		2,111,084,000
Cash and cash equivalents - end of year	1,496,485,000		1,121,705,000		1,342,257,000
Supplemental cash flow information:
Interest paid	49,259,000		49,259,000		49,259,000
Fixed maturities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	7,887,186,000		6,969,074,000		8,328,352,000
Purchases of fixed maturities and equities	8,872,874,000		8,067,087,000		10,549,343,000
Equity securities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	796,403,000		821,977,000		730,929,000
Purchases of fixed maturities and equities	695,456,000		830,323,000		619,533,000
Parent Company [Member]
Cash flows from operating activities
Net income (loss)	664,008,000		1,134,514,000		(520,291,000)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Equity in net (income) loss of subsidiaries	(756,513,000)		(1,215,106,000)		460,353,000
Other, net	27,397,000		30,573,000		7,663,000
Net cash provided by operating activities	(65,108,000)		(50,019,000)		(52,275,000)
Cash flows from investing activities
Advances to/from subsidiaries, net	666,444,000		190,017,000		3,511,000
Net issue of intercompany loans receivable and payable	14,473,000		132,797,000		379,676,000
Sales and redemptions of fixed maturities	0		184,516,000		446,452,000
Payments/ proceeds from trading securities [Line Items]
Sales and redemptions of short-term investments	0		8,543,000		154,473,000
Purchases of short-term investments	0		0		(99,955,000)
Dividends received from subsidiaries	0		200,000,000		0
Investments in subsidiaries	0		0		(860,000,000)
Foreign exchange forward contracts	0		3,000		(6,750,000)
Other, net	196,000		772,000		2,408,000
Net cash provided by (used in) investing activities	681,113,000		716,648,000		19,815,000
Cash flows from financing activities
Dividends paid to common and preferred shareholders	(103,311,000)		(217,615,000)		(205,784,000)
Repurchase of common shares	(546,617,000)		(504,991,000)		(413,737,000)
Issuance of common shares	51,111,000		34,323,000		16,041,000
Net proceeds from issuance of preferred shares	241,265,000		0		361,722,000
Redemption of preferred shares	(290,000,000)		0		0
Net cash used in financing activities	(647,552,000)		(688,283,000)		(241,758,000)
Effect of foreign exchange rate changes on cash	2,461,000		297,000		(3,107,000)
Decrease in cash and cash equivalents	(29,086,000)		(21,357,000)		(277,325,000)
Cash and cash equivalents - beginning of year	30,372,000		51,729,000		329,054,000
Cash and cash equivalents - end of year	1,286,000		30,372,000		51,729,000
Supplemental cash flow information:
Interest paid	1,528,000		579,000		743,000
Non-cash dividends received from subsidiary	1,100,000,000	[1]	200,000,000	[1]	274,000,000	[1]
Subsidiaries [Member]
Cash flows from financing activities
Repurchase of common shares	(169,000,000)	[2]
Supplemental cash flow information:
Payment Of Dividends By Subsidiary On Behalf Of Parent	$ 97,000,000	[2]

[1] The parent received non-cash dividends from its subsidiaries of $1,100 million, $200 million and $274 million for the years ended December 31, 2013, 2012 and 2011, respectively, which have been excluded from the Condensed Statements of Cash Flows—Parent Company Only.

[2] During the year ended December 31, 2013, dividends paid to common and preferred shareholders of $97 million and the repurchase of common shares of $169 million were paid by a subsidiary on behalf of the parent and have been excluded from the Condensed Statements of Cash Flows—Parent Company Only.