TWO Quarterly report pursuant to Section 13 or 15(d)

Available-for-sale Securities Classified by Rate Type (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	$ 12,672,233	$ 13,666,954
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Adjustable Rate	1,007,715	188,429
Available-for-sale Securities, Fixed Rate	8,710,223	10,823,674
Available-for-sale securities, at fair value	9,717,938	11,012,103
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Adjustable Rate	2,527,240	2,334,950
Available-for-sale Securities, Fixed Rate	427,055	319,901
Available-for-sale securities, at fair value	2,954,295	2,654,851
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Adjustable Rate	3,534,955	2,523,379
Available-for-sale Securities, Fixed Rate	9,137,278	11,143,575
Available-for-sale securities, at fair value	$ 12,672,233	$ 13,666,954