RESIDENTIAL INVESTMENT SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Unrealized Loss Position For:
Estimated Fair Value	$ 79,369,396	$ 58,742,859
Gross Unrealized Losses	$ (1,283,639)	$ (1,361,566)
Number of Securities (security) | security	2,025	1,422
Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 39,878,158	$ 52,465,045
Gross Unrealized Losses	$ (272,234)	$ (1,094,957)
Number of Securities (security) | security	1,114	1,368
Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 39,491,238	$ 6,277,814
Gross Unrealized Losses	$ (1,011,405)	$ (266,609)
Number of Securities (security) | security	911	54