Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 531	$ 702
Total Average Assets	211,478	202,599
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	2,260	2,405
Commercial Bank [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	201	333
Total Average Assets	81,083	79,034
Commercial Bank [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	699	811
Commercial Bank [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	2	2
Retail Bank [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	446	452
Total Average Assets	52,232	51,293
Retail Bank [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,268	1,234
Institutional Services and Wealth Management [ Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	128	110
Total Average Assets	3,636	3,655
Institutional Services and Wealth Management [ Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	377	390
Institutional Services and Wealth Management [ Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	3	3
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	(244)	(193)
Total Average Assets	74,527	68,617
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	(84)	(30)
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (5)	$ (5)