INVESTMENT OPERATIONS (Details 2) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Investments classified as available-for-sale
Amortized Cost	$ 24,687,276,000	$ 24,162,714,000
Gross Unrealized Gains	3,053,685,000	3,249,825,000
Gross Unrealized Losses	(200,023,000)	(140,780,000)
Fair Value	27,540,938,000	27,271,759,000
Total OTTI Recognized in OCI	5,921,000	(6,134,000)
Investments classified as held-to-maturity
Amortized Cost	315,000,000	300,000,000
Gross Unrealized Gains	19,579,000	19,163,000
Fair Value	334,579,000	319,163,000
Amortized Cost
Due after ten years	315,000,000
Total	315,000,000	300,000,000
Fair Value
Due after ten years	334,579,000
Fair Value	334,579,000	319,163,000
Fixed maturities
Investments classified as available-for-sale
Amortized Cost	24,251,881,000	23,674,016,000
Gross Unrealized Gains	3,038,682,000	3,237,382,000
Gross Unrealized Losses	(193,260,000)	(130,747,000)
Fair Value	27,097,303,000	26,780,651,000
Total OTTI Recognized in OCI	6,164,000	(6,134,000)
Investments classified as held-to-maturity
Trading securities	3,000,000,000	3,000,000,000
Amortized Cost
Due in one year or less	462,459,000
Due after one year through five years	4,482,491,000
Due after five years through ten years	6,611,666,000
Due after ten years	12,695,265,000
Total	24,251,881,000
Fair Value
Due in one year or less	469,358,000
Due after one year through five years	4,937,108,000
Due after five years through ten years	7,246,081,000
Due after ten years	14,444,756,000
Total	27,097,303,000
Residential mortgage-backed securities
Investments classified as available-for-sale
Amortized Cost	1,670,034,000	1,766,440,000
Gross Unrealized Gains	88,814,000	92,265,000
Gross Unrealized Losses	(40,939,000)	(19,375,000)
Fair Value	1,717,909,000	1,839,330,000
Total OTTI Recognized in OCI	6,353,000	(406,000)
Commercial mortgage-backed securities
Investments classified as available-for-sale
Amortized Cost	853,334,000	797,844,000
Gross Unrealized Gains	64,906,000	72,577,000
Gross Unrealized Losses	(2,085,000)	(598,000)
Fair Value	916,155,000	869,823,000
Other asset-backed securities
Investments classified as available-for-sale
Amortized Cost	1,013,575,000	1,023,649,000
Gross Unrealized Gains	17,325,000	12,788,000
Gross Unrealized Losses	(84,339,000)	(61,424,000)
Fair Value	946,561,000	975,013,000
Total OTTI Recognized in OCI	(189,000)	(241,000)
U.S. government-related securities
Investments classified as available-for-sale
Amortized Cost	1,142,772,000	1,099,001,000
Gross Unrealized Gains	66,003,000	71,537,000
Gross Unrealized Losses	(1,723,000)	(595,000)
Fair Value	1,207,052,000	1,169,943,000
Other government-related securities
Investments classified as available-for-sale
Amortized Cost	82,172,000	93,565,000
Gross Unrealized Gains	6,323,000	7,258,000
Gross Unrealized Losses	(18,000)	(45,000)
Fair Value	88,477,000	100,778,000
States, municipals, and political subdivisions
Investments classified as available-for-sale
Amortized Cost	1,179,373,000	1,188,077,000
Gross Unrealized Gains	254,478,000	255,900,000
Gross Unrealized Losses	(269,000)	(264,000)
Fair Value	1,433,582,000	1,443,713,000
Corporate bonds
Investments classified as available-for-sale
Amortized Cost	18,310,621,000	17,705,440,000
Gross Unrealized Gains	2,540,833,000	2,725,057,000
Gross Unrealized Losses	(63,887,000)	(48,446,000)
Fair Value	20,787,567,000	20,382,051,000
Total OTTI Recognized in OCI		(5,487,000)
Other
Investments classified as held-to-maturity
Amortized Cost	315,000,000	300,000,000
Gross Unrealized Gains	19,579,000	19,163,000
Fair Value	334,579,000	319,163,000
Amortized Cost
Total	315,000,000	300,000,000
Fair Value
Fair Value	334,579,000	319,163,000
Equity securities
Investments classified as available-for-sale
Amortized Cost	384,499,000	389,821,000
Gross Unrealized Gains	15,003,000	12,443,000
Gross Unrealized Losses	(6,763,000)	(10,033,000)
Fair Value	392,739,000	392,231,000
Total OTTI Recognized in OCI	(243,000)
Investments classified as held-to-maturity
Trading securities	22,400,000	19,600,000
Short-term investments
Investments classified as available-for-sale
Amortized Cost	50,896,000	98,877,000
Fair Value	50,896,000	98,877,000
Investments classified as held-to-maturity
Trading securities	$ 110,600,000	$ 118,900,000