Fair Value (Details 1) (Level 3 [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Summary of changes in the fair value of the Level III investments
Balance, beginning of period	$ 17,400,674	$ 12,522,304	$ 15,673,386	$ 12,162,364
Transfers into Level III	417,985	136,970	236,529	341,148
Transfers out of Level III	(287,740)	(309,701)	(885,519)	(414,643)
Purchases	1,602,082	1,388,647	2,721,598	2,854,784
Sales	(1,838,683)	(282,535)	(1,970,600)	(1,734,106)
Net realized gain (loss) on investments	326,647	(63,722)	305,058	(64,696)
Net change in unrealized appreciation (depreciation) on investments	(50,133)	193,733	490,380	440,845
Balance, end of period	17,570,832	13,585,696	17,570,832	13,585,696
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	298,950	285,449	580,390	444,437
Corporate debt bank debt [Member]
Summary of changes in the fair value of the Level III investments
Balance, beginning of period	2,720,357	1,355,999	1,978,637	1,330,000
Transfers into Level III	68,038	43,124	375,612	94,022
Transfers out of Level III	(186,414)	(70,097)	(219,645)	(82,690)
Purchases	189,629	278,966	703,629	658,257
Sales	(333,151)	(15,423)	(363,540)	(425,014)
Net realized gain (loss) on investments	9,510	(7,053)	9,893	11,630
Net change in unrealized appreciation (depreciation) on investments	(43,953)	55,683	(60,570)	54,994
Balance, end of period	2,424,016	1,641,199	2,424,016	1,641,199
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	115,529	31,629	(9,546)	27,314
Equities - common stock [Member]
Summary of changes in the fair value of the Level III investments
Balance, beginning of period	6,613,693	6,004,741	6,349,335	5,774,231
Transfers into Level III	286,535		464,639	161
Transfers out of Level III	(8,088)	(88,799)	(359,682)	(94,200)
Purchases	454,453	289,634	682,612	563,459
Sales	(28,096)	(21,774)	(84,730)	(173,435)
Net realized gain (loss) on investments	(32,686)	13,406	(61,025)	8,393
Net change in unrealized appreciation (depreciation) on investments	136,219	141,181	430,881	259,780
Balance, end of period	7,422,030	6,338,389	7,422,030	6,338,389
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	154,290	72,332	285,098	174,747
Equities - preferred stock [Member]
Summary of changes in the fair value of the Level III investments
Balance, beginning of period	1,100,388	715,237	1,133,725	735,855
Transfers into Level III	1,761		6,987	95
Transfers out of Level III	(11,873)	(57,408)	(100,064)	(57,408)
Purchases	32,109	615	43,561	8,236
Sales	(3,411)	(3,855)	(3,857)	(58,122)
Net realized gain (loss) on investments	989	1,710	(3,199)	(9,706)
Net change in unrealized appreciation (depreciation) on investments	(29,367)	10,946	13,443	48,295
Balance, end of period	1,090,596	667,245	1,090,596	667,245
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	(24,640)	7,096	14,295	22,841
Other [Member]
Summary of changes in the fair value of the Level III investments
Balance, beginning of period	18,839	14,545	18,824	16,176
Transfers into Level III				1
Transfers out of Level III		(1)		(1)
Purchases		824		1,322
Net change in unrealized appreciation (depreciation) on investments	1,126	(804)	1,141	(2,934)
Balance, end of period	19,965	14,564	19,965	14,564
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	1,126	(805)	1,141	(2,935)
Corporate debt all other [Member]
Summary of changes in the fair value of the Level III investments
Balance, beginning of period	3,570,969	3,323,699	3,155,241	3,321,051
Transfers into Level III	44,376	93,685	372,016	245,773
Transfers out of Level III	(81,365)	(92,461)	(200,775)	(179,409)
Purchases	293,499	392,345	412,072	1,064,645
Sales	(853,066)	(165,478)	(863,895)	(980,120)
Net realized gain (loss) on investments	95,070	(76,557)	100,293	(82,346)
Net change in unrealized appreciation (depreciation) on investments	(14,806)	(15,290)	79,725	70,349
Balance, end of period	3,054,677	3,459,943	3,054,677	3,459,943
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	20,447	166,539	132,093	205,468
Real estate [Member]
Summary of changes in the fair value of the Level III investments
Balance, beginning of period	3,376,428	1,108,083	3,037,624	985,051
Transfers into Level III	17,275	161	17,275	1,096
Transfers out of Level III		(935)	(5,353)	(935)
Purchases	632,392	426,263	879,724	558,865
Sales	(620,959)	(76,005)	(654,578)	(97,415)
Net realized gain (loss) on investments	253,764	4,772	259,096	7,333
Net change in unrealized appreciation (depreciation) on investments	(99,352)	2,017	25,760	10,361
Balance, end of period	3,559,548	1,464,356	3,559,548	1,464,356
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	$ 32,198	$ 8,658	$ 157,309	$ 17,002