Retirement Plans (Details Textuals) (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
	Jun. 14, 2019	Feb. 01, 2018	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer					$ 0
Bank Mutual Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 6	$ 31
RAP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 4
Bank Mutual
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effective Date of Acquisition		Feb. 01, 2018
Huntington National Bank
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effective Date of Acquisition	Jun. 14, 2019