Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Contingency [Line Items]
Income tax expense	$ 9	$ 7
Minimum
Income Tax Contingency [Line Items]
Reasonable possible decrease in unrecognized tax benefits	5
Maximum
Income Tax Contingency [Line Items]
Reasonable possible decrease in unrecognized tax benefits	$ 10