REPURCHASE ARRANGEMENTS AND SIMILAR BORROWINGS - Collateral and Rates (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2014 Maximum [Member]	Sep. 30, 2014 Quarter-End Borrowing Rates Adjusted For Effects Of Related Derivatives Held As Cash Flow Hedges [Member]	Dec. 31, 2013 Quarter-End Borrowing Rates Adjusted For Effects Of Related Derivatives Held As Cash Flow Hedges [Member]	Sep. 30, 2014 Agency Securities [Member]	Dec. 31, 2013 Agency Securities [Member]	Sep. 30, 2014 Agency Securities [Member] Borrowings With Maturities Of 30 Days Or Less [Member]	Dec. 31, 2013 Agency Securities [Member] Borrowings With Maturities Of 30 Days Or Less [Member]	Sep. 30, 2014 Agency Securities [Member] Borrowings With Maturities of 31 to 90 Days [Member]	Dec. 31, 2013 Agency Securities [Member] Borrowings With Maturities of 31 to 90 Days [Member]	Sep. 30, 2014 Agency Securities [Member] Borrowings With Maturities Greater Than 90 Days [Member]	Sep. 30, 2014 Agency Securities [Member] Similar Borrowings [Member]		Dec. 31, 2013 Agency Securities [Member] Similar Borrowings [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Maturity period of repurchase arrangements			P30D	P90D
Collateral Carrying Amount	$ 13,400,000	$ 13,120,000					$ 13,399,616	$ 13,123,757	$ 11,007,943	$ 12,169,534	$ 519,510	$ 951,966	$ 1,870,094	$ 2,069	[1]	$ 2,257	[1]
Accrued Interest Receivable							27,609	30,263	22,583	28,195	1,099	2,068	3,927	0	[1]	0	[1]
Borrowings Outstanding	12,749,762	12,482,900					12,749,762	12,482,900	10,471,646	11,578,211	497,530	902,432	1,778,517	2,069	[1]	2,257	[1]
Average Borrowing Rates (in hundredths)					0.52%	0.49%	0.33%	0.38%	0.30%	0.38%	0.31%	0.38%	0.52%	8.10%	[1]	8.09%	[1]
Average borrowings adjusted amount	$ 12,690,463	$ 12,510,701
Average borrowings rates adjusted for effects related cash flow derivatives (in hundredths)	0.51%	0.49%

[1] The maturity of structured financings is directly affected by prepayments on the related mortgage pass-through securities pledged as collateral and these financings are subject to redemption by the residual bondholders.