Pension Plans and Other Postretirement Benefits - Net Periodic Benefit Cost for Defined Benefit Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11	$ 18	$ 20
Interest cost on benefit obligation	115	82	62
Expected return on plan assets	(201)	(188)	(143)
Amortization of prior service cost (credit)		1	1
Recognized net actuarial (gain) loss	(2)	20	89
Net periodic pension (benefit) cost	$ (77)	$ (67)	$ 29
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 3	$ 1
Interest cost on benefit obligation	3	2	1
Amortization of prior service cost (credit)	(2)	(3)	(5)
Recognized net actuarial (gain) loss	$ (3)	(1)	(1)
Net periodic pension (benefit) cost		$ 1	$ (4)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense