Loans - Concentrations and Restrictions (Details) $ in Billions	3 Months Ended
	Mar. 31, 2020 USD ($)
Consumer | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage	19.00%
Commercial | Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, before allowance for credit loss	$ 2.8
Percentage of commercial & industrial loan portfolio	13.00%
Percentage contributed in total loan	8.00%
Commercial | Loans to Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, before allowance for credit loss	$ 5.7
Percentage of commercial & industrial loan portfolio	26.00%
Percentage contributed in total loan	17.00%
Commercial | Finance Insurance And Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial & industrial loan portfolio	39.00%