Pension and Postretirement Benefit Plans - Future Benefit Payments (Details) - Funded $ in Millions	Dec. 31, 2018 USD ($)
Qualified and Non-qualified Pension Benefits | United States
Future Pension and Postretirement Benefit Payments
2019 Benefit Payments	$ 1,094
2020 Benefit Payments	1,097
2021 Benefit Payments	1,105
2022 Benefit Payments	1,117
2023 Benefit Payments	1,130
Next five years	5,683
Qualified and Non-qualified Pension Benefits | International
Future Pension and Postretirement Benefit Payments
2019 Benefit Payments	240
2020 Benefit Payments	242
2021 Benefit Payments	258
2022 Benefit Payments	269
2023 Benefit Payments	289
Next five years	1,623
Postretirement Benefits
Future Pension and Postretirement Benefit Payments
2019 Benefit Payments	122
2020 Benefit Payments	130
2021 Benefit Payments	139
2022 Benefit Payments	147
2023 Benefit Payments	157
Next five years	$ 842