Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Retirement Benefits [Abstract]
Total net periodic defined benefit plan credit	$ (89)	$ (65)
Total defined contribution plans	421	435
Total pension and OPEB cost included in noninterest expense	$ 332	$ 370