Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			$ 25	$ 58		$ 58
Cash payments			(65)			(49)
Restructuring charges			630			124
Other			(541)			(108)
Restructuring reserve ending balance	$ 49		49			25
Restructuring and other charges (D)	119	$ (2)	630	20
Layoff costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			10	56		56
Cash payments			(61)			(47)
Restructuring charges			45			111
Other			50			(110)
Restructuring reserve ending balance	44		44			10
Restructuring and other charges (D)	(1)	$ (1)	(4)
Other exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			15	$ 2		2
Cash payments			(4)			(2)
Restructuring charges			585			13
Other			(591)			2
Restructuring reserve ending balance	5		5			15
Restructuring and other charges (D)			12
Employee Severance Cost, Reclassification Of Pension Costs
Restructuring Reserve [Roll Forward]
Other						119
Employee Severance Costs, Credit In Post-Retirement Costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)						(28)
Employee Severance, Reversal Of Prior Restructuring
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)						$ (19)
Elimination Of Life Insurance Benefits
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			(58)
Other, Pension Settlement Cost
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			8
Impairment Of Disks
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			428
Asset Impairment associated with the sale of business
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)	$ 102
Other Exit Costs, Impairment Of Intangibles And Property Plant and Equipment
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			24
Loss On Sale Related To Small Additive Business
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			12
Other Exit Cost Lease Termination Loss
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			12
Accelerated Depreciation
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			6
Other Exit Costs, Credit
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			2
Other Exit Costs, Reclassification Of Lease Exit Costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges (D)			$ (9)
Scenario, Forecast | Layoff costs
Restructuring Reserve [Roll Forward]
Cash payments					$ (15)