Management Agreement and Related Party Transactions (Details 2) (Affiliates, USD $)	Sep. 30, 2011 issuer	Dec. 31, 2010 issuer
Investments in affiliates
Aggregate par amount	$ 2,500,000,000	$ 2,400,000,000
Investment in affiliates as a percentage of total investment (as a percent)	30.00%	30.00%
Investment in affiliates, number of issuers	28	27
Corporate loans
Investments in affiliates
Par	2,200,000,000	2,100,000,000
Securities available-for-sale.
Investments in affiliates
Par	199,900,000	314,200,000
Equity investments, at estimated fair value
Investments in affiliates
Par	$ 58,600,000	$ 25,600,000