Commitments, Off-Balance Sheet Arrangements, Legal Proceedings and Regulatory Matters (Details Textuals) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	$ 25	$ 24
Loans Repurchased Under Make Whole Requests	$ 1
Loans Sold To Outside Investors Loss ReimbursementSettlement Paid	zero	negligible
Loans Sold To Outside Investors Original Amount	$ 10,800
Loans Sold To Outside Investors Remaining Outstanding Amount	7,000
Residential Mortgage Loans Sold With Recourse Risk	46	$ 44
Residential Mortgage Loans Sold With Credit Recourse Risk	60	73
UnconsolidatedProjectsLowIncomeHousing [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	132	147
Commitments Under Unconsolidated Projects	85	119
PrincipalInvestmentCommitment [Member]
Commitments, Off-Balance Sheet Arrangements, and Contingent Liabilities (Textuals) [Line Items]
Other Investments	$ 25	$ 23