Loans and Allowance for Loan Losses - Recorded Investment Amounts of TDRs at Date of Default (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	$ 42	$ 3
Minimum defaulting period	60 days
Commercial | Commercial and industrial
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	$ 40	0
Commercial | Commercial mortgage
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	1	0
Consumer | residential mortgage and home equity [Member]
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	1	3
Consumer Portfolio Segment [Member]
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	1	3
Commercial Portfolio Segment [Member]
Pre- and Post - modification recorded investments
Total troubled debt restructured loans at date of default	$ 41	$ 0