Loans and Allowance for Loan Losses - Recorded Investment Amounts of Troubled Debt Restructurings (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Troubled debt restructured loans
Minimum defaulting period	60 days
Total troubled debt restructured loans at date of default	$ 1
Commercial
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	1
Consumer
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	0
Home Equity and Other Consumer Loans [Member] | Consumer Loans
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	0
Commercial and industrial | Commercial Loans Portfolio Segment [Member]
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	0
Commercial mortgage | Commercial Loans Portfolio Segment [Member]
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	1
Residential mortgage | Consumer Loans
Troubled debt restructured loans
Total troubled debt restructured loans at date of default	$ 0