Restructuring - Restructuring Expense by Type (Details) - Organizational restructuring - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Restructuring Cost and Reserve [Line Items]
Cumulative Amounts Incurred to Date	$ 279
Severance benefits
Restructuring Cost and Reserve [Line Items]
Total restructuring expenses	(3)	$ 47
Cumulative Amounts Incurred to Date	55
Transition Costs
Restructuring Cost and Reserve [Line Items]
Total restructuring expenses	22	$ 36
Cumulative Amounts Incurred to Date	$ 224