Loans and Related Allowance for Credit Losses (Analysis of Changes in the Allowance for Credit Losses) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Changes in the Allowance for Credit Losses [Roll Forward]
Portfolio changes	$ 595
Economic/Qualitative Factors	2,143
Ending balance	6,440
Allowances for investment securities and other financial assets	98
Cumulative Effect, Period of Adoption, Adjusted Balance
Changes in the Allowance for Credit Losses [Roll Forward]
Beginning balance	3,702
Ending balance	$ 6,440