Investments (Details 4) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Schedule Of Available For Sale Securities
Available For Sale Securities Gross Unrealized Losses	$ 233,819	$ 319,131
Corporate Debt Securities Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	7,307,996	6,826,937
Available For Sale Securities Gross Unrealized Gains	470,307	436,384
Available For Sale Securities Gross Unrealized Losses	81,235	107,816
Available For Sale Securities Fair Value Disclosure	7,697,068	7,155,505
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	0	0
Percentage Of Total Available For Sale Securities	50.80%	50.00%
Canadian Provincial Governments Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	2,533,410	2,354,418
Available For Sale Securities Gross Unrealized Gains	677,586	672,951
Available For Sale Securities Gross Unrealized Losses	2,840	3,886
Available For Sale Securities Fair Value Disclosure	3,208,156	3,023,483
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	0	0
Percentage Of Total Available For Sale Securities	21.20%	21.10%
Residential Mortgage Backed Securities Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	1,320,758	1,443,892
Available For Sale Securities Gross Unrealized Gains	59,345	55,765
Available For Sale Securities Gross Unrealized Losses	14,319	26,580
Available For Sale Securities Fair Value Disclosure	1,365,784	1,473,077
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	(258)	(1,650)
Percentage Of Total Available For Sale Securities	9.00%	10.30%
Asset Backed Securities Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	415,637	440,752
Available For Sale Securities Gross Unrealized Gains	12,925	12,001
Available For Sale Securities Gross Unrealized Losses	51,642	61,544
Available For Sale Securities Fair Value Disclosure	376,920	391,209
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	(6,258)	(4,963)
Percentage Of Total Available For Sale Securities	2.50%	2.70%
Commercial Mortgage Backed Securities Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	1,333,832	1,353,279
Available For Sale Securities Gross Unrealized Gains	92,380	81,839
Available For Sale Securities Gross Unrealized Losses	67,107	97,265
Available For Sale Securities Fair Value Disclosure	1,359,105	1,337,853
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	(8,375)	(10,010)
Percentage Of Total Available For Sale Securities	9.00%	9.40%
US Government And Government Agencies And Authorities Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	191,048	199,129
Available For Sale Securities Gross Unrealized Gains	10,832	7,795
Available For Sale Securities Gross Unrealized Losses	602	708
Available For Sale Securities Fair Value Disclosure	201,278	206,216
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	0	0
Percentage Of Total Available For Sale Securities	1.30%	1.40%
US States And Political Subdivisions Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	192,368	170,479
Available For Sale Securities Gross Unrealized Gains	11,057	2,098
Available For Sale Securities Gross Unrealized Losses	5,061	8,117
Available For Sale Securities Fair Value Disclosure	198,364	164,460
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	0	0
Percentage Of Total Available For Sale Securities	1.30%	1.20%
Foreign Government Debt Securities Member | Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	746,298	556,136
Available For Sale Securities Gross Unrealized Gains	8,557	4,304
Available For Sale Securities Gross Unrealized Losses	7,723	7,646
Available For Sale Securities Fair Value Disclosure	747,132	552,794
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	0	0
Percentage Of Total Available For Sale Securities	4.90%	3.90%
Nonredeemable Preferred Stock Member | Equity Securities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	104,444	100,718
Available For Sale Securities Gross Unrealized Gains	5,337	4,130
Available For Sale Securities Gross Unrealized Losses	2,263	5,298
Available For Sale Securities Fair Value Disclosure	107,518	99,550
Percentage Of Total Available For Sale Securities	75.60%	71.00%
Equity Securities Other Member | Equity Securities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	34,237	34,832
Available For Sale Securities Gross Unrealized Gains	1,498	6,100
Available For Sale Securities Gross Unrealized Losses	1,027	271
Available For Sale Securities Fair Value Disclosure	34,708	40,661
Percentage Of Total Available For Sale Securities	24.40%	29.00%
Fixed Maturities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	14,041,347	13,345,022
Available For Sale Securities Gross Unrealized Gains	1,342,989	1,273,137
Available For Sale Securities Gross Unrealized Losses	230,529	313,562
Available For Sale Securities Fair Value Disclosure	15,153,807	14,304,597
Accumulated Other Comprehensive Income Loss Other Than Temporary Impairment Not Credit Loss Net Of Tax Availableforsale Debt Securities	(14,891)	(16,623)
Percentage Of Total Available For Sale Securities	100.00%	100.00%
Equity Securities Member
Schedule Of Available For Sale Securities
Available For Sale Securities Amortized Cost	138,681	135,550
Available For Sale Securities Gross Unrealized Gains	6,835	10,230
Available For Sale Securities Gross Unrealized Losses	3,290	5,569
Available For Sale Securities Fair Value Disclosure	$ 142,226	$ 140,211
Percentage Of Total Available For Sale Securities	100.00%	100.00%