Short-Term Borrowings (Summary of Short-Term Borrowings and Weighted-Average Rates) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Short Term Debt
Federal funds purchased	$ 1,925	$ 174
Other short-term borrowings	573	4,012
Federal Funds Purchased
Short Term Debt
Federal funds purchased	1,925	174
Short-term borrowings, average	1,509	557
Short-term borrowings, maximum month-end balance	$ 2,684	$ 1,495
Short-term borrowngs, rate	2.40%	1.37%
Short-term borrowings, average rate	1.97%	1.01%
Other Short Term Borrowings
Short Term Debt
Other short-term borrowings	$ 573	$ 4,012
Short-term borrowings, average	1,611	3,158
Short-term borrowings, maximum month-end balance	$ 6,313	$ 6,307
Short-term borrowngs, rate	1.95%	1.28%
Short-term borrowings, average rate	1.82%	0.96%