Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Taxes Other Information [Line Items]
Income Tax Expense (Benefit)	$ 147	$ 159
Effective Income Tax Rate Reconciliation, Percent	19.00%	25.00%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Other Tax Expense (Benefit)	$ 4	$ 22
Excess Tax Benefit from Share-based Compensation, Financing Activities	20
Adjustment to Deferred Taxes Remeasurement Benefit Related to 2017 Tax Act	19
Tax Expense (Benefit) from Valuation Allowance Adjustment	(35)
Deferred Tax Assets, Valuation Allowance	$ (179)		$ (143)