Retirement Programs - Pension and Postretirement Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain						$ (9)
Settlement charges	$ 6	$ 40	$ 51					$ 0
Amount recognized in Net pension and OPEB cost (benefit), excluding service cost						(32)	$ (4)	(4)
Termination charge						17
Defined Benefit Plan, Benefit Obligation, Payment for Settlement			91
Pensions
Defined Benefit Plan Disclosure [Line Items]
Service cost						142	74	46
Interest cost						261	128	103
Expected return on plan assets						(462)	(219)	(161)
Net amortization and deferral						61	71	68
Curtailment gain						8	0	0
Settlement charges			$ 2	$ 10	$ 4	97	14	2
Amount recognized in Net pension and OPEB cost (benefit), excluding service cost						(35)	(6)	12
Settlement gains from divestitures						0	(44)	0
Net periodic benefit cost (benefit)						107	24	58
OPEB
Defined Benefit Plan Disclosure [Line Items]
Service cost						2	2	3
Interest cost						7	5	5
Expected return on plan assets						0
Net amortization and deferral						(4)	3	(3)
Curtailment gain						0	0	(18)
Settlement charges						0
Amount recognized in Net pension and OPEB cost (benefit), excluding service cost						3	2	(16)
Settlement gains from divestitures						0	0	0
Net periodic benefit cost (benefit)						5	4	$ (13)
Defined Benefit Plan, Benefit Obligation, Payment for Settlement						$ 0	$ 0