DEBT - Short-Term Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Short-Term Borrowings:
Commercial paper	$ 9,940	$ 9,989
Other borrowings	34,512	20,712
Total short-term borrowings	44,452	30,701
Collateralized short-term advances from Federal Home Loan Bank	$ 23,800	$ 12,000
Commercial paper
Short-Term Borrowings:
Weighted average coupon	1.28%	0.79%
Other borrowings
Short-Term Borrowings:
Weighted average coupon	1.62%	1.39%