Schedule II - Condensed Financial Information of Registrant (Balance Sheets (Parent Company)) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets:
Cash and cash equivalents	$ 905,670,000	$ 911,742,000	$ 642,952,000	$ 515,430,000
Fixed maturity securities available for sale at fair value (cost $244,921 and $244,804 at December 31, 2011 and 2010, respectively)	11,943,956,000	11,312,037,000
Equity securities available for sale	376,022,000	443,439,000
Deferred Federal income taxes	447,041,000	433,062,000
Current Federal income taxes	0	9,670,000
Property, furniture and equipment at cost, less accumulated depreciation	267,227,000	262,275,000
Other assets	242,135,000	195,696,000
Total assets	20,155,896,000	18,403,873,000
Liabilities:
Other liabilities	981,626,000	866,229,000
Deferred Federal income taxes	507,296,000	435,897,000
Junior subordinated debentures	243,206,000	242,997,000
Senior notes	1,871,535,000	1,500,503,000
Total liabilities	15,820,430,000	14,442,991,000
Stockholders' equity:
Preferred stock	0	0
Common stock	47,024,000	47,024,000
Additional paid-in capital	945,166,000	941,109,000
Retained earnings (including accumulated undistributed net income of subsidiaries of $3,384,149 and $3,309,411 at December 31, 2011 and 2010, respectively)	4,817,807,000	4,491,162,000
Accumulated other comprehensive income	465,631,000	354,851,000
Treasury stock, at cost	(1,969,411,000)	(1,880,790,000)
Total stockholders' equity	4,335,466,000	3,960,882,000
Total liabilities and stockholders' equity	20,155,896,000	18,403,873,000
Equity securities available for sale at cost $0 in 2011 and 2010	308,175,000	342,393,000
Parent Company [Member]
Assets:
Cash and cash equivalents	162,972,000	270,637,000	29,476,000	117,648,000
Fixed maturity securities available for sale at fair value (cost $244,921 and $244,804 at December 31, 2011 and 2010, respectively)	286,597,000	247,537,000
Equity securities available for sale	25,699,000	81,811,000
Investment in subsidiaries	5,979,539,000	5,334,461,000
Due from subsidiaries	106,334,000	0
Current Federal income taxes	0	15,137,000
Property, furniture and equipment at cost, less accumulated depreciation	7,895,000	6,595,000
Other assets	10,710,000	6,951,000
Total assets	6,579,746,000	5,963,129,000
Liabilities:
Due to subsidiaries	0	141,492,000
Other liabilities	176,416,000	146,823,000
Deferred Federal income taxes	31,914,000	12,283,000
Current Federal income taxes	8,253,000	0
Junior subordinated debentures	243,206,000	242,997,000
Senior notes	1,813,740,000	1,466,178,000
Total liabilities	2,273,529,000	2,009,773,000
Stockholders' equity:
Preferred stock	0	0
Common stock	47,024,000	47,024,000
Additional paid-in capital	945,166,000	941,109,000
Retained earnings (including accumulated undistributed net income of subsidiaries of $3,384,149 and $3,309,411 at December 31, 2011 and 2010, respectively)	4,817,807,000	4,491,162,000
Accumulated other comprehensive income	465,631,000	354,851,000
Treasury stock, at cost	(1,969,411,000)	(1,880,790,000)
Total stockholders' equity	4,306,217,000	3,953,356,000
Total liabilities and stockholders' equity	6,579,746,000	5,963,129,000
Fixed maturity securities available for sale at cost: $244,921 and $244,804 in 2011 and 2010, respectively	281,708	244,921	244,804
Equity securities available for sale at cost $0 in 2011 and 2010	0	0	0
Accumulated undistributed net income of subsidiaries of $3,384,149 and $3,309,411 in 2011 and 2010, respectively	$ 4,023,780	$ 3,329,079	$ 3,309,411