SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Unrealized Loss Position For:
Estimated Fair Value	$ 86,556,058	$ 79,369,396
Gross Unrealized Losses	$ (3,860,199)	$ (1,283,639)
Number of Securities (security) | security	3,446	2,025
Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 46,457,384	$ 39,878,158
Gross Unrealized Losses	$ (1,401,491)	$ (272,234)
Number of Securities (security) | security	2,213	1,114
Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	$ 40,098,674	$ 39,491,238
Gross Unrealized Losses	$ (2,458,708)	$ (1,011,405)
Number of Securities (security) | security	1,233	911