MANAGEMENT AGREEMENT AND RELATED PARTY TRANSACTIONS (Details 2) (Affiliates, USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Issuer	Dec. 31, 2012 Issuer
Investments in affiliates
Aggregate par amount	$ 2,000,000,000	$ 2,100,000,000
Investment in affiliates as a percentage of total investment	30.00%	29.00%
Investment in affiliates, number of issuers	31	32
Corporate loans
Investments in affiliates
Par	1,900,000,000	2,000,000,000
Corporate debt securities
Investments in affiliates
Par	39,700,000	39,300,000
Equity investments, at estimated fair value
Investments in affiliates
Par	81,000,000	73,800,000
Joint ventures and partnerships
Investments in affiliates
Aggregate cost amount	$ 157,600,000	$ 137,600,000