Summary of Significant Accounting Policies and Nature of Operations (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) type_of_lease shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)
Significant Accounting Policies
securities held to maturity transferred to securities available for sale	$ 170	$ 0	$ 0
Common stock, share issued (in shares) | shares	132,076,912	131,935,124
Loans placed on nonaccrual status when past due term (days)	90 days
Interest accrual period (days)	90 days
Financing Receivable, Threshold Period Past Due, Writeoff	120 days
Consecutive payment period for accrual status	6 months
Number of types of leases offered to customers | type_of_lease	2
Accounting Standards Update 2016-13 [Member]
Significant Accounting Policies
Day one impact to allowance for credit losses	$ 199
increase to deferred tax assets	52
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 147