RESIDENTIAL INVESTMENT SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Unrealized Loss Position For:
Estimated Fair Value	$ 85,172,108	$ 79,369,396
Gross Unrealized Losses	$ (3,074,602)	$ (1,283,639)
Number of Securities (security) | security	2,432	2,025
Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 47,494,769	$ 39,878,158
Gross Unrealized Losses	$ (1,222,887)	$ (272,234)
Number of Securities (security) | security	1,497	1,114
Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 37,677,339	$ 39,491,238
Gross Unrealized Losses	$ (1,851,715)	$ (1,011,405)
Number of Securities (security) | security	935	911