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	Dec. 31, 2018	Dec. 31, 2017
Community Development Investments [Member]
Portion of Other Assets Not Qualified for Tax Credits	$ (68)	$ (59)
Loans Issued by the Company to the Limited Partnerships	422	354
Unfunded Equity Commitment	639	$ 627
Renewable Energy Program [Member]
Unfunded Equity Commitment	$ 52