Fair Value Measurements (Summary Of Quantitative Information About Level 3 Fair Value Measurements) (Details) - Discounted Cash Flow [Member] $ in Millions	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Mortgage Servicing Rights [Member] \| Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	$ 296	$ 345	$ 418
Recurring Fair Value Measurements [Member] \| Residential Mortgage Servicing Rights [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted Average CPR	0.081	0.074	0.044
Option-Adjusted Spread	4.80%	5.20%	5.70%
Recurring Fair Value Measurements [Member] \| Residential Mortgage Servicing Rights [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted Average CPR	0.312	0.261	0.426
Option-Adjusted Spread	9.50%	10.20%	15.00%
Recurring Fair Value Measurements [Member] \| Residential Mortgage Servicing Rights [Member] \| Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Weighted Average CPR	0.156	0.120	0.090
Option-Adjusted Spread	5.60%	6.20%	7.60%