Fair Value Measurements - Schedule of Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	$ 230	$ 249
Mortgage servicing assets excluded from OREO	23
Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	230	249
Loans held for sale	62	93
Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral-dependent loans	96	152
Loans held for sale	3	0
Level 3 | Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	4	(4)
Insignificant level 3 assets, net of liabilities	3	2
Loans held for sale	0	0
Level 3 | Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral-dependent loans	96	152
Loans held for sale	3	0
Market comparable pricing | Level 3 | Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential)	$ 10	$ 10
Market comparable pricing | Level 3 | Recurring | Comparability factor | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.7430	0.6800
Market comparable pricing | Level 3 | Recurring | Comparability factor | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.9900	0.9500
Market comparable pricing | Level 3 | Recurring | Comparability factor | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.8462	0.7748
Market comparable pricing | Level 3 | Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans held for sale	$ 3	$ 0
Discounted cash flow | Level 3 | Recurring | Interest rate
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	$ 3	$ (4)
Discounted cash flow | Level 3 | Recurring | Interest rate | Probability of default | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0002	0.0002
Discounted cash flow | Level 3 | Recurring | Interest rate | Probability of default | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Discounted cash flow | Level 3 | Recurring | Interest rate | Probability of default | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0460	0.0500
Discounted cash flow | Level 3 | Recurring | Interest rate | Loss given default | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0	0
Discounted cash flow | Level 3 | Recurring | Interest rate | Loss given default | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Discounted cash flow | Level 3 | Recurring | Interest rate | Loss given default | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.500	0.500
Fair value of collateral | Level 3 | Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral-dependent loans	$ 96	$ 152
Fair value of collateral | Level 3 | Nonrecurring | Credit and liquidity discount | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral-dependent loans, measurement input	0	0
Fair value of collateral | Level 3 | Nonrecurring | Credit and liquidity discount | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral-dependent loans, measurement input	1.0000	1.0000
Fair value of collateral | Level 3 | Nonrecurring | Credit and liquidity discount | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral-dependent loans, measurement input	0.3300	0.3300
Appraised value | Level 3 | Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
OREO and other Level 3 assets	$ 9	$ 14