Pensions Benefit Plans and Other Postretirement Benefits - Components of Net Periodic Pension and Postretirement Cost (Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefit Plans
Amortization:
Accumulated benefit obligation	$ 2,735	$ 3,126
U.S. Pension Plans
Components of net periodic pension cost
Service cost	14	15	$ 24
Interest cost	78	90	96
Expected asset return	(128)	(149)	(170)
Amortization:
Actuarial loss	57	67	74
Net periodic pension cost	21	23	24
Settlement cost	176	98
Annuity contract purchase for settlement of pension obligation	369	200
Canadian Pension Plans
Amortization:
Settlement cost	27
Annuity contract purchase for settlement of pension obligation	123
Pension Plan of the United Kingdom
Amortization:
Settlement cost	15
Non-U.S. Pension Plans
Components of net periodic pension cost
Service cost	15	16	15
Interest cost	40	44	44
Expected asset return	(63)	(65)	(67)
Amortization:
Actuarial loss	16	13	15
Net periodic pension cost	8	8	7
U.S Postretirement Benefit Plans
Components of net periodic pension cost
Interest cost	4	4	4
Amortization:
Actuarial loss	2	2	2
Prior service cost	(8)	(8)	(8)
Net amortization	(6)	(6)	(6)
Net periodic pension cost	(2)	(2)	(2)
Non-U.S. Postretirement Benefit Plans
Components of net periodic pension cost
Service cost	1	1	1
Interest cost	3	3	3
Amortization:
Net periodic pension cost	$ 4	$ 4	$ 4