Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Schedule of Automotive Industry Outstanding Loans and Total Exposure) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Total automotive loans	$ 8,663	$ 9,428
Total automotive exposure	12,035	12,440
Automotive Production
Concentration Risk [Line Items]
Total automotive loans	1,249	1,331
Total automotive exposure	2,358	2,396
Automotive Dealer
Concentration Risk [Line Items]
Total automotive loans	7,414	8,097
Total automotive exposure	$ 9,677	$ 10,044