Fair Value Accounting - Schedule of Assets Measured at Fair Value on a Non-Recurring Basis (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2026	Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans, valuation allowance	$ 32	$ 32
Other real estate, writedowns	12
Level 1 \| Fair Value, Measurements, Nonrecurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	0	0
Other real estate	0	0
Level 2 \| Fair Value, Measurements, Nonrecurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	0	0
Other real estate	0	0
Level 3 \| Fair Value, Measurements, Nonrecurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	100	80
Other real estate	$ 17	$ 8