Derivatives (Net Gains (Losses) Recorded in the Consolidated Statements of Income Relating to Free-Standing Derivative Instruments Used For Customer Accommodation) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest Rate Contract | Customer Contracts | Corporate Banking Revenue
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	$ 7	$ 5
Interest Rate Contract | Interest Rate Lock Commitments | Mortgage Banking Revenue
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	13	22
Commodity Contract | Customer Contracts | Corporate Banking Revenue
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	2	1
Commodity Contract | Fair Value Adjustments on Hedges and Derivative Contracts | Other noninterest expense
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	0	1
Foreign Exchange Contract | Customer Contracts | Corporate Banking Revenue
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	14	13
Foreign Exchange Contract | Customer Contracts | Other Noninterest Income
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	(2)	0
Foreign Exchange Contract | Fair Value Adjustments on Hedges and Derivative Contracts | Other noninterest expense
Derivative Instruments, Gain (Loss)
Net gains (losses) recorded in earnings	$ 1	$ 1