Income Taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes Other Information [Line Items]
Income Tax Expense (Benefit)	$ 548	$ 532	$ 805
Effective Income Tax Rate Reconciliation, Percent	16.50%	19.00%	30.00%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 113
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	22	$ 17
Unrecognized Tax Benefits, Income Tax Penalties Accrued	5	10
Adjustment to Deferred Taxes Remeasurement Benefit Related to 2017 Tax Act	55	303
Deferred Tax Assets, Valuation Allowance	85	$ 143
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 50