Restructuring Restructuring - Accrued Liability for Restructuring Expense (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Organizational restructuring
Restructuring Reserve [Roll Forward]
Accrued liability as of January 1, 2018	$ 21
Provision	201
Payments	(167)
Accrued liability as of December 31, 2018	55
Organizational restructuring | Severance Benefits
Restructuring Reserve [Roll Forward]
Accrued liability as of January 1, 2018	12
Provision	39
Payments	(21)
Accrued liability as of December 31, 2018	30
Organizational restructuring | Other Costs
Restructuring Reserve [Roll Forward]
Accrued liability as of January 1, 2018	9
Provision	162
Payments	(146)
Accrued liability as of December 31, 2018	25
2016 Restructuring
Restructuring Reserve [Roll Forward]
Accrued liability as of January 1, 2018	24
Provision	8
Payments	(20)
Accrued liability as of December 31, 2018	12
2016 Restructuring | Severance Benefits
Restructuring Reserve [Roll Forward]
Accrued liability as of January 1, 2018	8
Provision	0
Payments	(4)
Accrued liability as of December 31, 2018	4
2016 Restructuring | Transition Costs
Restructuring Reserve [Roll Forward]
Accrued liability as of January 1, 2018	14
Provision	0
Payments	(6)
Accrued liability as of December 31, 2018	8
2016 Restructuring | Other Costs
Restructuring Reserve [Roll Forward]
Accrued liability as of January 1, 2018	2
Provision	8
Payments	(10)
Accrued liability as of December 31, 2018	$ 0