REPURCHASE ARRANGEMENTS AND SIMILAR BORROWINGS - Collateral and Rates (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]	Sep. 30, 2013 Quarter-End Borrowing Rates Adjusted For Effects Of Related Derivatives Held As Cash Flow Hedges [Member]	Dec. 31, 2012 Quarter-End Borrowing Rates Adjusted For Effects Of Related Derivatives Held As Cash Flow Hedges [Member]	Sep. 30, 2013 Agency Securities [Member]	Dec. 31, 2012 Agency Securities [Member]	Sep. 30, 2013 Agency Securities [Member] Borrowings With Maturities Of 30 Days Or Less [Member]	Dec. 31, 2012 Agency Securities [Member] Borrowings With Maturities Of 30 Days Or Less [Member]	Sep. 30, 2013 Agency Securities [Member] Borrowings With Maturities Greater Than 30 Days [Member]	Dec. 31, 2012 Agency Securities [Member] Borrowings With Maturities Greater Than 30 Days [Member]	Sep. 30, 2013 Agency Securities [Member] Similar Borrowings [Member]		Dec. 31, 2012 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	$ 13,290,000	$ 13,450,000					$ 13,290,055	$ 13,453,159	$ 13,246,162	$ 13,406,253	$ 41,598	$ 44,060	$ 2,295	[1]	$ 2,846	[1]
Accrued Interest Receivable							28,785	32,858	28,737	32,807	48	51	0	[1]	0	[1]
Borrowings Outstanding							12,618,571	12,784,238	12,579,977	12,739,872	36,299	41,520	2,295	[1]	2,846	[1]
Average Borrowing Rates (in hundredths)					0.47%	0.65%	0.36%	0.47%	0.35%	0.47%	0.45%	0.57%	8.08%	[1]	8.12%	[1]
Average borrowings adjusted amount	$ 12,862,572	$ 13,228,535
Average borrowings rates adjusted for effects related cash flow derivatives (in hundredths)	0.49%	0.63%

[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.