Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	$ 839
Deferred Tax Liabilities, Net	2
Income Tax Examination, Penalties and Interest Expense	0	$ 0
Income Tax Examination, Interest Accrued	0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	0
Income Tax Examination, Penalties Accrued	0
Capital Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Net	$ 459