| In millions, except per share items | Dec-31-15 | Dec-31-14 | Dec-31-13 | Dec-31-12 |
| | 10-K | 10-K | 10-K | 10-K |
| Operating revenues | | | | |
| Contract drilling revenues | 564 | 557 | | |
| Other revenues | 16 | 10 | | |
| Total operating revenues | 580 | 567 | 526 | 569 |
| Total operating revenues growth | 2.3% | 7.8% | -7.6% | |
| Costs and expenses | | | | |
| Operating and maintenance | 245 | 248 | | |
| |
| Depreciation | | | | |
| General and administrative | 24 | 20 | | |
| Total costs and expenses | 337 | 334 | | |
| Loss on impairment | -356 | | | |
| Loss on disposal of assets | -1 | | | |
| Operating income (loss) | -114 | 233 | | |
| Operating margin | -19.7% | 41.1% | | |
| |
| Other income (loss) | | | | |
| Interest income | 2 | 3 | | |
| Interest expense | -1.0 | -1.0 | | |
| Income (loss) before income tax expense | -113 | 235 | 212 | 279 |
| Income tax expense | 14 | 20 | | |
| Tax rate | | 8.5% | 0.0% | 0.0% |
| Net income (loss) | -127 | 215 | | |
| Net income (loss) attributable to noncontrolling interest | -56 | 44 | | |
| Net income (loss) attributable to controlling interest | -71 | 36 | | |
| |
| Earnings (loss) per unit—basic | | | | |
| Earnings (loss) per unit—basic | | | | |
| Earnings (loss) per unit—diluted | | | | |
| Earnings (loss) per unit—diluted | | | | |
| Weighted‑average units outstanding—basic | | | | |
| Weighted-average units outstanding—basic (in units) | | | | |
| Weighted‑average units outstanding—diluted | | | | |
| Weighted-average units outstanding—diluted (in units) | | | | |