RESIDENTIAL INVESTMENT SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Unrealized Loss Position For:
Estimated Fair Value	$ 82,218,276	$ 79,369,396
Gross Unrealized Losses	$ (3,487,521)	$ (1,283,639)
Number of Securities (security) | security	2,462	2,025
Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 43,845,297	$ 39,878,158
Gross Unrealized Losses	$ (1,386,377)	$ (272,234)
Number of Securities (security) | security	1,360	1,114
Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 38,372,979	$ 39,491,238
Gross Unrealized Losses	$ (2,101,144)	$ (1,011,405)
Number of Securities (security) | security	1,102	911