SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Unrealized Loss Position For:
Estimated Fair Value	$ 17,513,412	$ 65,552,879
Gross Unrealized Losses	$ (159,777)	$ (2,285,609)
Number of Securities (security) | security	551	2,189
Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 3,524,012	$ 22,418,036
Gross Unrealized Losses	$ (17,042)	$ (432,352)
Number of Securities (security) | security	45	713
Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 13,989,400	$ 43,134,843
Gross Unrealized Losses	$ (142,735)	$ (1,853,257)
Number of Securities (security) | security	506	1,476