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

Available-for-sale Securities Classified by Rate Type (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Adjustable Rate	$ 2,095,657	$ 2,687,117
Available-for-sale Securities, Fixed Rate	9,337,538	11,653,985
Available-for-sale securities, at fair value	11,433,195	14,341,102
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Adjustable Rate	114,929	128,285
Available-for-sale Securities, Fixed Rate	8,911,071	11,164,032
Available-for-sale securities, at fair value	9,026,000	11,292,317
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Adjustable Rate	1,980,728	2,558,832
Available-for-sale Securities, Fixed Rate	426,467	489,953
Available-for-sale securities, at fair value	$ 2,407,195	$ 3,048,785