Postretirement Benefit Plans - Assumed Future Benefits Payments (Details) $ in Millions	Dec. 31, 2017 USD ($)
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
2018 payment	$ 140
2019 payment	111
2020 payment	83
2021 payment	90
2022 payment	87
2023 - 2027 payment	410
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
2018 payment	30
2019 payment	31
2020 payment	31
2021 payment	30
2022 payment	30
2023 - 2027 payment	139
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
2018 payment	86
2019 payment	87
2020 payment	89
2021 payment	90
2022 payment	94
2023 - 2027 payment	$ 495