SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Unrealized Loss Position For:
Estimated Fair Value	$ 54,652,187	$ 65,552,879
Gross Unrealized Losses	$ (1,223,601)	$ (2,285,609)
Number of Securities (security) | security	1,602	2,189
Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 12,188,284	$ 22,418,036
Gross Unrealized Losses	$ (197,039)	$ (432,352)
Number of Securities (security) | security	89	713
Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 42,463,903	$ 43,134,843
Gross Unrealized Losses	$ (1,026,562)	$ (1,853,257)
Number of Securities (security) | security	1,513	1,476