Income Taxes Income Taxes - Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Beginning Balance	$ 426	$ 749	$ 741
Decreases related to positions taken on items from prior years	(14)	(167)	(44)
Increases related to positions taken on items from prior years	5	77	74
Increases related to positions taken in the current year	6	54	9
Settlement of uncertain tax positions with tax authorities	(18)	(9)	(13)
Unrecognized Tax Benefits, Impact of Internal Reorganizations	0	(278)	0
Decreases due to expiration of statutes of limitations	(7)	0	(5)
Exchange (gain) loss	(3)	0	(13)
Unrecognized Tax Benefits, Ending Balance	395	426	749
Total unrecognized tax benefits that, if recognized, would impact the effective tax rate	156	188	45
Total amount of interest and penalties (benefit) recognized in Provision for income taxes on continuing operations	(2)	(4)	11
Total accrual for interest and penalties associated with unrecognized tax benefits	$ 18	$ 24	$ 45