Short-Term Borrowings - Summary of Short-Term Borrowings (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Securities sold under repurchase agreements	$ 278	$ 251
Federal Home Loan Bank advances	2,255	2,230
Federal funds purchased	575	1,535
Subordinated notes	108	113
Total short-term borrowings	$ 3,216	$ 4,129
Short-term advances, overnight maturities	0.00%	57.20%
Short-term advances	$ 1,500	$ 1,000
Short-term advances, percentage bearing fixed interest rate	64.50%	42.80%