BORROWED FUNDS - Short Term Debt (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Total short-term borrowed funds		$ 1,809	$ 2,671
Federal funds purchased
Short-term Debt [Line Items]
Total short-term borrowed funds		0	460
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Total short-term borrowed funds		315	355
Other short-term borrowed funds
Short-term Debt [Line Items]
Total short-term borrowed funds	[1]	1,494	1,856
CBNA Global Bank Note Program
Short-term Debt [Line Items]
Total short-term borrowed funds		1,500	750
Unamortized deferred issuance costs and/or discounts		(2)	(1)
Other basis adjustments		$ (14)	$ (4)

[1] March 31, 2018 includes $1.5 billion of debt issued under CBNA’s Global Bank Note Program maturing within one year, with unamortized deferred issuance costs and/or discounts of ($2) million and other basis adjustments of ($14) million. December 31, 2017 includes $750 million of debt issued under CBNA’s Global Bank Note Program maturing within one year, with unamortized deferred issuance costs and/or discounts of ($1) million and other basis adjustments of ($4) million.