Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Income tax expense			$ 658			$ 658
Accumulated foreign earnings, provisional income tax expense			676
Noncurrent income taxes payable				$ 462	$ 495
Additional foreign withholding tax			53
Deferred tax asset, provisional income tax benefit			82
Effective tax rate				23.30%	24.50%	48.40%
Discrete tax expense (benefit)	$ (21)
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance		$ (37)
Effective tax rate, tax credit, foreign		$ 22
Effective tax rate, share-based compensation, excess tax benefit, amount				$ 28	$ 10	$ 50
Accrual foreign withhold taxes				62	71
Undistributed earnings of foreign subsidiaries				5,700
Unrecognized tax benefits that would impact effective tax rate				267
Possible decrease in unrecognized tax benefits resulting from ongoing audits				56
Accrual for interest and penalties related to income tax matters				$ 19	$ 25
Deferred Tax Asset Related to Performance-based Compensation
Income Tax Examination [Line Items]
Write-off of deferred tax assets			$ 11