Income Taxes - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	1.00%
Effective Income Tax Rate Reconciliation, Change in the Discrete Items, Amount	$ 12	$ 8
Tax Cuts and Jobs Act of 2017 Transition Tax Adjustment for Accumulated Foreign Earnings Provisional Amount	10
Excess Tax Benefit on Stock Based Payments	$ 4	$ 7
Tax Cuts and Jobs Act of 2017, transition tax for accumulated foreign earnings, provisional amount			$ 51
Effective Income Tax Rate Reconciliation, Change as a result of the Discrete Items, Percent	0.60%