Retirement and Postretirement Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Aug. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Periodic Benefit Costs
Decrease to benefit obligation	$ 178
Pension Benefit
Net Periodic Benefit Costs
Service cost		$ 0	$ 2	$ 4	$ 6
Interest cost		4	4	12	12
Expected return on plan assets		(7)	(6)	(19)	(18)
Recognized actuarial loss		2	2	4	6
Additional settlement cost		3	0	3	0
Total		2	2	4	6
Postretirement Benefit
Net Periodic Benefit Costs
Service cost		5	5	17	15
Interest cost		8	9	26	29
Expected return on plan assets		0	0	0	0
Recognized actuarial loss		2	3	12	11
Additional settlement cost		0	0	0	0
Total		15	17	55	55
Defined benefit plans
Net Periodic Benefit Costs
Employer contributions		$ 2	$ 1	$ 4	$ 3