INVESTMENT OPERATIONS - Additional Information (Details)		3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 15, 2016 note	Jun. 30, 2017 USD ($) position subsidiary	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) position subsidiary	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) subsidiary
Investment [Line Items]
Gross unrealized loss greater than twelve months		$ 704,728,000		$ 704,728,000		$ 1,196,195,000
Total positions that were in an unrealized loss position | position		1,846		1,846
Fair Value		$ 37,785,148,000		$ 37,785,148,000		36,570,665,000
Available-for-sale securities, amortized cost		38,337,534,000		38,337,534,000		$ 38,233,986,000
Other-than-temporary impairments on held-to-maturity securities		$ 0	$ 0	$ 0	$ 0
Red Mountain and Steel City
Investment [Line Items]
Number of wholly owned subsidiaries that were determined to be VIEs | subsidiary		2		2		2
Red Mountain
Investment [Line Items]
Ownership through an affiliate (as a percent)				100.00%
Risk of loss related to the VIE limited to the entity's investment		$ 10,000		$ 10,000
Payments made				$ 0
Steel City
Investment [Line Items]
Ownership through an affiliate (as a percent)				100.00%
Risk of loss related to the VIE limited to the entity's investment		10,000		$ 10,000
Payments made				0
Number of notes issued | note	3
Below investment grade
Investment [Line Items]
Trading securities		240,200,000		240,200,000
Fair Value		1,900,000,000		1,900,000,000
Available-for-sale securities, amortized cost		1,900,000,000		1,900,000,000
Securities not publicly traded		372,100,000		372,100,000
Fixed maturities
Investment [Line Items]
Trading securities		2,700,000,000		2,700,000,000		$ 2,600,000,000
Other-than-temporary impairments related to fixed maturities or equity securities that the Company intended to sell or expected to be required to sell		0	0	0	0
Fair Value		36,681,824,000		36,681,824,000		35,543,477,000
Available-for-sale securities, amortized cost		37,253,204,000		37,253,204,000		37,192,864,000
Gross unrealized gains		80,605,000		80,605,000		30,385,000
Gross unrealized losses		22,575,000		22,575,000		67,222,000
Equity securities
Investment [Line Items]
Trading securities		5,200,000		5,200,000		7,100,000
Other-than-temporary impairments related to fixed maturities or equity securities that the Company intended to sell or expected to be required to sell		0	$ 0	0	$ 0
Gross unrealized loss greater than twelve months		4,670,000		4,670,000		6,412,000
Fair Value		782,130,000		782,130,000		747,406,000
Available-for-sale securities, amortized cost		763,136,000		763,136,000		761,340,000
Short-term investments
Investment [Line Items]
Trading securities		45,800,000		45,800,000		52,600,000
Fair Value		321,194,000		321,194,000		279,782,000
Available-for-sale securities, amortized cost		321,194,000		321,194,000		279,782,000
Residential mortgage-backed securities
Investment [Line Items]
Gross unrealized loss greater than twelve months		2,178,000		2,178,000		4,117,000
Fair Value		2,001,137,000		2,001,137,000		1,898,483,000
Available-for-sale securities, amortized cost		2,006,404,000		2,006,404,000		1,913,413,000
Commercial mortgage-backed securities
Investment [Line Items]
Gross unrealized loss greater than twelve months		3,658,000		3,658,000		4,013,000
Fair Value		1,832,129,000		1,832,129,000		1,811,470,000
Available-for-sale securities, amortized cost		1,852,497,000		1,852,497,000		1,850,620,000
Other asset-backed securities
Investment [Line Items]
Gross unrealized loss greater than twelve months		11,263,000		$ 11,263,000		$ 11,407,000
Percentage of underlying collateral of student-loan backed auction rate securities guaranteed by the Federal Family Education Loan Program (FFELP), minimum				97.00%		97.00%
Fair Value		1,182,003,000		$ 1,182,003,000		$ 1,211,533,000
Available-for-sale securities, amortized cost		1,179,284,000		1,179,284,000		1,210,490,000
Other government-related securities
Investment [Line Items]
Gross unrealized loss greater than twelve months		7,694,000		7,694,000		11,890,000
Fair Value		251,504,000		251,504,000		239,921,000
Available-for-sale securities, amortized cost		253,115,000		253,115,000		253,182,000
States, municipals, and political subdivisions
Investment [Line Items]
Gross unrealized loss greater than twelve months		36,331,000		36,331,000		41,749,000
Fair Value		1,689,321,000		1,689,321,000		1,656,503,000
Available-for-sale securities, amortized cost		1,755,780,000		1,755,780,000		1,760,837,000
Corporate securities
Investment [Line Items]
Gross unrealized loss greater than twelve months		636,930,000		636,930,000		1,114,729,000
Fair Value		28,336,554,000		28,336,554,000		27,371,565,000
Available-for-sale securities, amortized cost		$ 28,790,475,000		$ 28,790,475,000		$ 28,801,768,000