Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available for sale	$ 45,364	$ 27,556
Derivative assets	1,962	1,798
Mortgage servicing assets excluded from OREO	67	40
Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available for sale	45,364	27,556
Other investments	105	81
Derivative assets	1,962	1,798
Fair Value, Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral dependent loans	28	108
Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available for sale	0	13
Other investments	10	14
Derivative assets	39	91
Level 3 | Fair Value, Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral dependent loans	28	108
Other securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available for sale	0	13
Other securities | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available for sale	0	13
Other securities | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available for sale	0	13
Principal investments: Direct | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	1	1
Principal investments: Direct | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	1	1
Discounted cash flows | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	9	13
Discounted cash flows | Other securities | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available for sale	0	13
Market comparable pricing | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential)	11	11
Fair value of underlying collateral | Level 3 | Fair Value, Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral dependent loans	28	108
Appraised value | Level 3 | Fair Value, Nonrecurring
Fair Value, Option, Quantitative Disclosures [Line Items]
OREO and other assets	13	16
Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	33	56
Credit | Discounted cash flows | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	1	1
Derivative liabilities	7	11
Other | Discounted cash flows | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets	$ 5	$ 32
Discount rate | Discounted cash flows | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available-for-sale, measurement input		0.1509
Discount rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments, measurement input	0.1443	0.1390
Discount rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments, measurement input	0.1756	0.1704
Discount rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments, measurement input	0.1630	0.1547
Discount rate | Fair value of underlying collateral | Level 3 | Fair Value, Nonrecurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral dependent loans, measurement input	0	0
Discount rate | Fair value of underlying collateral | Level 3 | Fair Value, Nonrecurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral dependent loans, measurement input	0.1000	1.0000
Discount rate | Fair value of underlying collateral | Level 3 | Fair Value, Nonrecurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Collateral dependent loans, measurement input	0.0800	0.3600
Marketability discount | Discounted cash flows | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available-for-sale, measurement input		0.3000
Marketability discount | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments, measurement input		0.3000
Volatility factor | Discounted cash flows | Level 3 | Fair Value, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Securities available-for-sale, measurement input		0.4400
Volatility factor | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments, measurement input		0.5200
Comparability factor | Market comparable pricing | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.6450	0.6450
Comparability factor | Market comparable pricing | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.9730	0.9904
Comparability factor | Market comparable pricing | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans, net of unearned income (residential), measurement input	0.9424	0.9417
Probability of default | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0002	0.0002
Probability of default | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Probability of default | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0888	0.0790
Probability of default | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0002	0.0002
Derivative liabilities, measurement input	0.0002	0.0002
Probability of default | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Derivative liabilities, measurement input	1	1
Probability of default | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0600	0.0470
Derivative liabilities, measurement input	0.0328	0.1545
Internal risk rating | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Internal risk rating | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	19	19
Internal risk rating | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	13.34	9.68
Internal risk rating | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Derivative liabilities, measurement input	1	1
Internal risk rating | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	19	19
Derivative liabilities, measurement input	19	19
Internal risk rating | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	9.02	10.48
Derivative liabilities, measurement input	6.92	8.56
Loss given default | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0	0
Loss given default | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Loss given default | Interest rate | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.50	0.48
Loss given default | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0	0
Derivative liabilities, measurement input	0	0
Loss given default | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	1	1
Derivative liabilities, measurement input	1	1
Loss given default | Credit | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.49	0.49
Derivative liabilities, measurement input	0.50	0.43
Loan closing rates | Other | Discounted cash flows | Level 3 | Fair Value, Recurring | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.0264	0.3695
Loan closing rates | Other | Discounted cash flows | Level 3 | Fair Value, Recurring | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.9970	0.9968
Loan closing rates | Other | Discounted cash flows | Level 3 | Fair Value, Recurring | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative assets, measurement input	0.8570	0.7751