Commitments and Contingencies - Environmental Matters (Details) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Commitments and Contingencies Disclosure [Abstract] | ||
| Accrued liabilities for remediation | $ 112 | $ 114 |
| Receivables for recoverable costs | $ 45 | $ 45 |