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, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Total automotive loans		$ 6,785	$ 8,663
Total automotive exposure		11,920	12,035
Automotive Production
Concentration Risk [Line Items]
Total automotive loans	[1]	1,093	1,249
Total automotive exposure	[1]	2,267	2,358
Automotive Dealer
Concentration Risk [Line Items]
Total automotive loans		5,692	7,414
Total automotive exposure		$ 9,653	$ 9,677

[1] Excludes PPP loans.