Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Effective income tax rate	(10.80%)	29.90%	6.90%	28.50%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent						35.00%
State and Local Jurisdiction
Income Tax Examination [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 445		$ 445
Scenario, Forecast [Member]
Income Tax Examination [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%
Tax Year 2013-2014 [Member]
Income Tax Examination [Line Items]
Effective Income Tax Rate Reconciliation, Tax Settlement, Domestic, Amount			$ 412