Income Taxes - Cumulative Effect, Period of Adoption, Adjustment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020
Income Taxes.
Interest and penalties related to unrecognized tax benefits, expense (benefit) recognized on a gross basis	$ 21	$ 33	$ 12
Interest and penalties related to unrecognized tax benefits, accrued on a gross basis	126	102
Deferred tax assets valuation allowance	$ 135	$ 158
Effective tax rate (as a percent)	19.60%	19.80%	23.40%
Increase in effective income tax rate from prior reporting period to current reporting period (as a percent)	(0.20%)	(3.60%)
Previously undistributed earnings from non-U.S. subsidiaries permanently reinvested	$ 15,000
Reinvested earnings that may be repatriated from non-U.S. subsidiaries				$ 5,000
Undistributed earnings from non-U.S. subsidiaries permanently reinvested	$ 10,000
Statutory U.S. tax rate	21.00%	21.00%	21.00%
Tax Cuts and Jobs Act of 2017 measurement period adjustment			$ 176
Period of time over which TCJA transition tax on certain unrepatriated earnings of foreign subsidiaries may be paid			8 years
Tax Cuts and Jobs Act of 2017 transition tax in current accrued income taxes payable	$ 69	$ 33
Tax Cuts and Jobs Act of 2017 transition tax long term income taxes payable	$ 584	$ 653