Income Taxes - Analysis of the Effective Tax Rate (Details) - USD ($) $ in Millions			12 Months Ended
Jan. 01, 2018	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal income tax rate	21.00%	35.00%	21.00%	35.00%	35.00%
Net tax effects of:
State income taxes, net of federal income tax benefit			7.00%	5.00%	6.00%
Tax-exempt interest income			(1.00%)	(1.00%)	(1.00%)
Effective Income Tax Rate Reconciliation, Deduction, Amount			(2.00%)	(3.00%)	(3.00%)
Amortization of LIHC investments			12.00%	14.00%	10.00%
Tax credits			(25.00%)	(21.00%)	(18.00%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount			(2.00%)	(8.00%)	0.00%
Effective Income Tax Rate Reconciliation, State Refunds, Percent			(5.00%)	0.00%	0.00%
Other			0.00%	1.00%	2.00%
Effective tax rate			5.00%	22.00%	31.00%
One Time Tax Benefit from Change in Federal Corporate Tax Rate			$ 101

Effective Income Tax Rate Reconciliation, State Refunds, Percent

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One time tax benefit from the Tax Cuts & Jobs Act which reduced the federal corporate income tax rate from 35% to 21% effective January 1, 2018.

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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 attributable to deductions. Including, but not limited to, extraterritorial income exclusion deduction, qualified production activity deduction, dividend deduction, deduction for dividend paid to employee stock ownership plan, Medicare prescription drug benefit subsidy deduction, and other deductions.

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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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