Retirement Plans and Other Retiree Benefits - Expected Contributions and Benefit Payments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Estimated future voluntary employer contributions in next fiscal year	$ 75
Expected benefit payments from company assets	82
Total benefit payments [Abstract]
2018	219
2019	222
2020	227
2021	228
2022	238
2023-2027	1,209
Other Retiree Benefit Plans
Total benefit payments [Abstract]
2018	45
2019	46
2020	46
2021	47
2022	48
2023-2027	250
United States | Pension Plans
Total benefit payments [Abstract]
2018	137
2019	141
2020	144
2021	143
2022	151
2023-2027	737
International | Pension Plans
Total benefit payments [Abstract]
2018	37
2019	35
2020	37
2021	38
2022	39
2023-2027	$ 222