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

Available-for-Sale Securities, at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	$ 21,059,377	$ 21,220,819
Available-for-sale securities, at fair value, pledged as collateral for borrowings	20,858,710	20,990,890
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	14,074,434	13,920,721
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	3,287,343	3,616,967
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	680,387	701,037
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at fair value	$ 3,017,213	$ 2,982,094