INCOME TAXES - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective income tax rate reconciliation [Abstract]
Income taxes computed at the federal statutory rate	$ 27,856	$ 29,005	$ 37,914
Benefit of REIT status	(27,854)	(29,003)	(37,913)
Income taxes computed on income of Capstead’s sole taxable REIT subsidiary	2	2	1
Alternative minimum tax credit refund receivable	(1,941)
Change in deferred asset balance due to change in corporate tax rate	29
Other change in net deferred income tax assets	(31)	$ (2)	$ (1)
Income tax (benefit) provision recorded in miscellaneous other revenue (expense)	$ (1,941)