Loans and Related Allowance for Credit Losses (Analysis of Changes in the Allowance for Credit Losses) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Changes in the Allowance for Credit Losses [Roll Forward]
Portfolio changes	$ 498
Economic/Qualitative Factors	1,745
Ending balance	5,945
Allowances for investment securities and other financial assets	109
Cumulative Effect, Period of Adoption, Adjusted Balance
Changes in the Allowance for Credit Losses [Roll Forward]
Beginning balance	3,702
Ending balance	$ 5,945