Certain Transfers of Financial Assets and Variable Interest Entities Tax Credit Variable Interest Entities (Additional Information) (Details) - Variable Interest Entity, Not Primary Beneficiary [Member] - Limited Partner [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Community Development Investments [Member]
Portion of Other Assets Not Qualified for Tax Credits	$ (67)	$ (68)
Loans Issued by the Company to the Limited Partnerships	470	422
Unfunded Equity Commitment	593	639
Renewable Energy Program [Member]
Unfunded Equity Commitment	$ 186	$ 52