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Income Taxes - Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax at U.S. federal statutory tax rate	21.00%	21.00%	35.00%
State taxes, net of federal benefit	3.10%	3.20%	2.20%
Non-deductible expenses	1.60%	2.20%	0.70%
Low-income housing, new markets tax credits, and other credits	(5.20%)	(4.00%)	(5.80%)
Tax-exempt interest and other nontaxable income	(0.80%)	(0.70%)	(1.50%)
IRS method changes	0.00%	(3.90%)	0.00%
Impacts of the Tax Act	0.00%	(0.30%)	32.20%
Other, net	(0.20%)	0.20%	(1.30%)
Effective tax rate	19.50%	17.70%	61.50%

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Percentage of the difference between the effective income tax rate and U.S. federal statutory tax rate related to IRS method changes

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Effective income tax rate reconciliation, Impact of the Tax Act

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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