Fair Value of Financial Assets and Liabilities - Measurements of Assets and Liabilities on Recurring Basis (Details) - USD ($)
$ in Millions |
Jun. 30, 2018 |
Dec. 31, 2017 |
| Assets: |
|
|
| Restricted funds |
$ 29
|
$ 28
|
| Rabbi trust investments |
15
|
15
|
| Deposits |
3
|
4
|
| Mark-to-market derivative asset |
9
|
|
| Other investments |
3
|
3
|
| Total assets |
59
|
50
|
| Liabilities: |
|
|
| Deferred compensation obligations |
17
|
17
|
| Mark-to-market derivative liability |
3
|
3
|
| Total liabilities |
20
|
20
|
| Total net assets (liabilities) |
39
|
30
|
| Level 1 |
|
|
| Assets: |
|
|
| Restricted funds |
29
|
28
|
| Rabbi trust investments |
15
|
15
|
| Deposits |
3
|
4
|
| Mark-to-market derivative asset |
0
|
|
| Other investments |
3
|
3
|
| Total assets |
50
|
50
|
| Liabilities: |
|
|
| Deferred compensation obligations |
17
|
17
|
| Mark-to-market derivative liability |
0
|
0
|
| Total liabilities |
17
|
17
|
| Total net assets (liabilities) |
33
|
33
|
| Level 2 |
|
|
| Assets: |
|
|
| Restricted funds |
0
|
0
|
| Rabbi trust investments |
0
|
0
|
| Deposits |
0
|
0
|
| Mark-to-market derivative asset |
9
|
|
| Other investments |
0
|
0
|
| Total assets |
9
|
0
|
| Liabilities: |
|
|
| Deferred compensation obligations |
0
|
0
|
| Mark-to-market derivative liability |
3
|
3
|
| Total liabilities |
3
|
3
|
| Total net assets (liabilities) |
6
|
(3)
|
| Level 3 |
|
|
| Assets: |
|
|
| Restricted funds |
0
|
0
|
| Rabbi trust investments |
0
|
0
|
| Deposits |
0
|
0
|
| Mark-to-market derivative asset |
0
|
|
| Other investments |
0
|
0
|
| Total assets |
0
|
0
|
| Liabilities: |
|
|
| Deferred compensation obligations |
0
|
0
|
| Mark-to-market derivative liability |
|
0
|
| Total liabilities |
0
|
0
|
| Total net assets (liabilities) |
$ 0
|
$ 0
|