Fair Value (Fair Value Measurements- Recurring Quantitative Information) (Details) - Fair Value, Recurring $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 111,263	$ 103,035
Financial and nonfinancial liabilities, fair value disclosure	(3,934)	(3,506)
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	5,611	5,137
Financial and nonfinancial liabilities, fair value disclosure	(302)	(318)
Total recurring assets net of recurring liabilities - fair value	5,309	4,819
Level 3 | Loans held for sale | Commercial mortgage loans held for sale | Discounted Cash Flow, Spread Over the Benchmark Curve
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 56	$ 57
Level 3 | Loans held for sale | Commercial mortgage loans held for sale | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	6.20%	6.30%
Level 3 | Loans held for sale | Commercial mortgage loans held for sale | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	63.50%	52.75%
Level 3 | Loans held for sale | Commercial mortgage loans held for sale | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	40.38%	34.06%
Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 1,316	$ 1,365
Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	1.55%	2.42%
Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 194	$ 199
Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	1.97%	2.91%
Level 3 | Loans - Residential real estate | Discounted cash flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 130	$ 132
Level 3 | Loans - Residential real estate | Consensus Pricing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 429	$ 434
Level 3 | Loans - Residential real estate | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	3.60%	3.60%
Level 3 | Loans - Residential real estate | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	100.00%	100.00%
Level 3 | Loans - Residential real estate | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	81.50%	82.10%
Level 3 | Loans - Residential real estate | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and liquidity discount		17.50%
Level 3 | Loans - Residential real estate | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and liquidity discount		97.00%
Level 3 | Loans - Residential real estate | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and liquidity discount		57.70%
Level 3 | Loans - Home equity | Consensus Pricing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 20	$ 21
Level 3 | Loans - Home equity | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	3.60%	3.60%
Level 3 | Loans - Home equity | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	100.00%	100.00%
Level 3 | Loans - Home equity | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative default rate	85.50%	88.50%
Level 3 | Loans - Home equity | Consensus Pricing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 132	$ 60
Level 3 | Loans - Home equity | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and liquidity discount	4.70%
Level 3 | Loans - Home equity | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and liquidity discount	92.00%
Level 3 | Loans - Home equity | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit and liquidity discount	44.00%
Level 3 | Equity investments | Multiple of adjusted earnings
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 1,343	$ 1,263
Level 3 | Equity investments | Multiple of adjusted earnings | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Multiple of earnings	0.040	0.050
Level 3 | Equity investments | Multiple of adjusted earnings | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Multiple of earnings	0.201	0.159
Level 3 | Equity investments | Multiple of adjusted earnings | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Multiple of earnings	0.088	0.087
Level 3 | Mortgage Servicing Rights | Commercial mortgage loans held for sale | Discounted cash flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 701	$ 569
Level 3 | Mortgage Servicing Rights | Residential mortgage loans held for sale | Discounted cash flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 979	$ 673
Level 3 | Mortgage Servicing Rights | Residential mortgage loans held for sale | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	3.83%	3.25%
Level 3 | Mortgage Servicing Rights | Residential mortgage loans held for sale | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	28.93%	27.83%
Level 3 | Mortgage Servicing Rights | Residential mortgage loans held for sale | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread over the benchmark curve	9.44%	9.22%
Level 3 | Derivative | Visa Class B Swap | Discounted cash flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial and nonfinancial liabilities, fair value disclosure	$ (201)	$ (252)
Estimated growth rate of Visa Class A share price	16.00%	16.00%
Level 3 | Derivative | Visa Class B Swap | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated conversion factor of Class B shares into Class A shares	162.30%	162.30%
Level 3 | Insignificant Assets, Net of Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring assets - fair value	$ 210
Financial and nonfinancial liabilities, fair value disclosure		$ 298
Measurement Input, Constant Prepayment Rate | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.010	0.010
Measurement Input, Constant Prepayment Rate | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.376	0.376
Measurement Input, Constant Prepayment Rate | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.102	0.086
Measurement Input, Constant Prepayment Rate | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.010	0.010
Measurement Input, Constant Prepayment Rate | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.400	0.220
Measurement Input, Constant Prepayment Rate | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.084	0.074
Measurement Input, Constant Prepayment Rate | Level 3 | Mortgage Servicing Rights | Commercial mortgage loans held for sale | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.041	0.040
Measurement Input, Constant Prepayment Rate | Level 3 | Mortgage Servicing Rights | Commercial mortgage loans held for sale | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.136	0.161
Measurement Input, Constant Prepayment Rate | Level 3 | Mortgage Servicing Rights | Commercial mortgage loans held for sale | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.049	0.049
Measurement Input, Constant Prepayment Rate | Level 3 | Mortgage Servicing Rights | Residential mortgage loans held for sale | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.000	0.000
Measurement Input, Constant Prepayment Rate | Level 3 | Mortgage Servicing Rights | Residential mortgage loans held for sale | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.314	0.775
Measurement Input, Constant Prepayment Rate | Level 3 | Mortgage Servicing Rights | Residential mortgage loans held for sale | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.107	0.211
Measurement Input, Constant Default Rate | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.000	0.000
Measurement Input, Constant Default Rate | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.188	0.122
Measurement Input, Constant Default Rate | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.060	0.047
Measurement Input, Constant Default Rate | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.014	0.010
Measurement Input, Constant Default Rate | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.060	0.060
Measurement Input, Constant Default Rate | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.029	0.033
Measurement Input, Loss Severity | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.250	0.250
Measurement Input, Loss Severity | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.957	0.957
Measurement Input, Loss Severity | Level 3 | Securities available for sale | Residential mortgage-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.486	0.488
Measurement Input, Loss Severity | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.300	0.300
Measurement Input, Loss Severity | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	1.000	1.000
Measurement Input, Loss Severity | Level 3 | Securities available for sale | Asset-backed | Priced By A Third Party Vendor Using Discounted Cash Flow Pricing Model | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, measurement input	0.553	0.581
Measurement Input, Loss Severity | Level 3 | Loans - Residential real estate | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.080	0.080
Measurement Input, Loss Severity | Level 3 | Loans - Residential real estate | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.000	0.000
Measurement Input, Loss Severity | Level 3 | Loans - Residential real estate | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	1.000	1.000
Measurement Input, Loss Severity | Level 3 | Loans - Residential real estate | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.100	0.112
Measurement Input, Loss Severity | Level 3 | Loans - Home equity | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.000	0.000
Measurement Input, Loss Severity | Level 3 | Loans - Home equity | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.984	0.984
Measurement Input, Loss Severity | Level 3 | Loans - Home equity | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.315	0.333
Measurement Input, Discount Rate | Level 3 | Loans - Residential real estate | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.032	0.032
Measurement Input, Discount Rate | Level 3 | Loans - Residential real estate | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.048	0.048
Measurement Input, Discount Rate | Level 3 | Loans - Residential real estate | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.068	0.068
Measurement Input, Discount Rate | Level 3 | Loans - Residential real estate | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.051	0.051
Measurement Input, Discount Rate | Level 3 | Loans - Home equity | Consensus Pricing | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.048	0.048
Measurement Input, Discount Rate | Level 3 | Loans - Home equity | Consensus Pricing | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.068	0.068
Measurement Input, Discount Rate | Level 3 | Loans - Home equity | Consensus Pricing | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.062	0.063
Measurement Input, Discount Rate | Level 3 | Mortgage Servicing Rights | Commercial mortgage loans held for sale | Discounted cash flow | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.055	0.047
Measurement Input, Discount Rate | Level 3 | Mortgage Servicing Rights | Commercial mortgage loans held for sale | Discounted cash flow | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.076	0.078
Measurement Input, Discount Rate | Level 3 | Mortgage Servicing Rights | Commercial mortgage loans held for sale | Discounted cash flow | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing asset, measurement input	0.074	0.073