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	Mar. 31, 2019	Dec. 31, 2018
Community Development Investments [Member]
Portion of Other Assets Not Qualified for Tax Credits	$ (69)	$ 68
Loans Issued by the Company to the Limited Partnerships	503	422
Unfunded Equity Commitment	579	639
Renewable Energy Program [Member]
Unfunded Equity Commitment	$ 0	$ 52