Retirement Benefits - Assumptions (Details)
|
12 Months Ended |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Retirement benefits other than pension |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Pension cost |
4.20%
|
4.40%
|
4.10%
|
| Benefit obligation at year end |
3.70%
|
4.20%
|
4.40%
|
| Expected return on assets |
8.25%
|
8.25%
|
8.25%
|
| U.S. Plans |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Pension cost |
4.30%
|
4.50%
|
4.10%
|
| Benefit obligation at year end |
3.70%
|
4.30%
|
4.50%
|
| Expected return on assets |
7.25%
|
7.50%
|
7.50%
|
| Non-U.S. Plans |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Pension cost |
3.70%
|
5.10%
|
5.10%
|
| Benefit obligation at year end |
3.50%
|
3.70%
|
5.10%
|
| Expected return on assets |
5.50%
|
5.65%
|
5.58%
|
| Average rate of increase in salaries - pension cost |
2.70%
|
3.80%
|
3.90%
|
| Average rate of increase in salaries - benefit obligation at year end |
2.60%
|
2.70%
|
3.80%
|
| UMWA Plans |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Pension cost |
4.10%
|
4.40%
|
4.00%
|
| Benefit obligation at year end |
3.60%
|
4.10%
|
4.40%
|
| Black Lung and Other Plans |
|
|
|
| Defined Benefit Plan Disclosure [Line Items] |
|
|
|
| Pension cost |
3.90%
|
4.20%
|
3.70%
|
| Benefit obligation at year end |
3.50%
|
3.90%
|
4.20%
|