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

Available-for-Sale Securities, at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	$ 20,199,094	$ 13,128,857
Available-for-sale securities, at fair value, pledged as collateral for borrowings	19,989,068	13,117,329
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	13,057,102	8,274,507
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	3,972,963	2,742,630
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	524,306	209,337
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	$ 2,644,723	$ 1,902,383