Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets, carryforwards
Tax credit carry forwards	$ 378,000,000
Uncertain tax liability	25,000,000
State tax credits	33,000,000
AMT tax credit carryforward	17,000,000
Net valuation allowance	0
Income Tax Uncertainties [Abstract]
Unrecognized tax positions that would affect the effective tax rate	98,000,000	$ 33,000,000	$ 9,000,000
Income Tax Examination, Interest Accrued	2,000,000
Income Tax Examination, Penalties Accrued	3,000,000
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	23,000,000
Domestic Tax Authority
Deferred tax assets, carryforwards
Operating loss carry forward	16,000,000
State and Local Jurisdiction
Deferred tax assets, carryforwards
Operating loss carry forward	$ 4,000,000