Loan Sale and Servicing Activities and Variable Interest Entities (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Liability related to investments in low income housing tax credits	$ 1,100	$ 600
Low Income Housing Tax Credit Investments
Other Tax Benefits Recognized Low Income Housing Tax Credit Investments	100
Cumulative effect of adopting ASU 2014-01 | Low Income Housing Tax Credit Investments
Amortization Recognized Low Income Housing Tax Credit Investments	200
Tax Credits Recognized Low Income Housing Tax Credit Investments	$ 200