Retirement Programs - Schedule of Pension and OPEB Net Periodic Benefit Costs (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net pension and OPEB cost (benefit)	$ 15	$ 2
Pensions
Defined Benefit Plan Disclosure [Line Items]
Service cost	39	12
Interest cost	68	26
Expected return on plan assets	(119)	(42)
Net amortization and deferral	14	18
Settlement charge (a)	51	0
Net pension and OPEB cost (benefit)	14	2
Net periodic benefit cost	53	14
After-tax pension settlement charges	$ 38
Settlement charges per diluted share (in dollars per share)	$ 0.07
OPEB
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	0
Interest cost	2	1
Expected return on plan assets		0
Net amortization and deferral	(1)	(1)
Settlement charge (a)	0	0
Net pension and OPEB cost (benefit)	1	0
Net periodic benefit cost	2	$ 0
United States | Nonqualified Plan | Pensions
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	$ 91