Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	$ 2,739	$ 1,962
Insignificant level 3 assets, net of liabilities	1	9
Mortgage servicing assets excluded from OREO	1	67
Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	2,739	1,962
Loans held for sale	114	281
Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	37	28
Loans held for sale	51	0
Level 3 \| Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	45	39
Loans held for sale	0	0
Level 3 \| Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	37	28
Loans held for sale	51	0
Valuation, Market Comparable Pricing \| Level 3 \| Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential)	11	11
Valuation, Market Comparable Pricing \| Level 3 \| Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans held for sale	$ 51	$ 0
Valuation, Market Comparable Pricing \| Measurement Input, Comparability Adjustment \| Level 3 \| Recurring \| Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.6450	0.6450
Valuation, Market Comparable Pricing \| Measurement Input, Comparability Adjustment \| Level 3 \| Recurring \| Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.9788	0.9730
Valuation, Market Comparable Pricing \| Measurement Input, Comparability Adjustment \| Level 3 \| Recurring \| Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.9233	0.9424
Valuation, Fair Value Of Underlying Collateral \| Level 3 \| Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	$ 37	$ 28
Valuation, Fair Value Of Underlying Collateral \| Measurement Input, Discount Rate \| Level 3 \| Nonrecurring \| Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans, measurement input	0	0
Valuation, Fair Value Of Underlying Collateral \| Measurement Input, Discount Rate \| Level 3 \| Nonrecurring \| Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans, measurement input	0.6500	0.1000
Valuation, Fair Value Of Underlying Collateral \| Measurement Input, Discount Rate \| Level 3 \| Nonrecurring \| Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans, measurement input	0.1900	0.0800
Valuation, Appraised Value \| Level 3 \| Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
OREO and other Level 3 assets	$ 11	$ 13
Interest rate \| Valuation Technique, Discounted Cash Flow \| Level 3 \| Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	$ 43	$ 33
Interest rate \| Valuation Technique, Discounted Cash Flow \| Measurement Input, Default Rate \| Level 3 \| Recurring \| Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0002	0.0002
Interest rate \| Valuation Technique, Discounted Cash Flow \| Measurement Input, Default Rate \| Level 3 \| Recurring \| Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Interest rate \| Valuation Technique, Discounted Cash Flow \| Measurement Input, Default Rate \| Level 3 \| Recurring \| Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.1170	0.0888
Interest rate \| Valuation Technique, Discounted Cash Flow \| Measurement Input, Loss Given Default \| Level 3 \| Recurring \| Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0	0
Interest rate \| Valuation Technique, Discounted Cash Flow \| Measurement Input, Loss Given Default \| Level 3 \| Recurring \| Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Interest rate \| Valuation Technique, Discounted Cash Flow \| Measurement Input, Loss Given Default \| Level 3 \| Recurring \| Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.500	0.500

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