Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
	Jan. 01, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Reconciliation [Line Items]
Statutory rate of income taxes		21.00%		35.00%	21.00%	35.00%
Operating loss carryforwards subject to SRLY tax rules will expire unutilized at December 31, 2018		$ 19			$ 19
Tax Cuts and Jobs Act of 2017
Income Tax Reconciliation [Line Items]
Statutory rate of income taxes	21.00%
Decrease in net deferred tax asset resulting from the changes in the Tax Cuts and Jobs Act of 2017			$ 83