| In millions, except per share items | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 | Dec-31-13 | Dec-31-12 | Dec-31-11 | Dec-31-10 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K/A | 10-K | 10-K |
| Net income | 79.0 | 27.1 | -54.2 | 44.6 | 377.7 | 2.6 | -40.1 | -10.6 |
| Depreciation and amortization [+] | 262.8 | 237.8 | 94.4 | 35.4 | -4.2 | 5.4 | 61.4 | 20.1 |
| Depreciation | 263.7 | 241.6 | 97.7 | 36.4 | 6.4 | 5.4 | 61.4 | 2.6 |
| Amortization of intangible assets | -0.8 | -3.8 | -3.2 | -1.0 | -10.6 | | | 11.8 |
| Asset impairment charges | 37.8 | 11.2 | | | | | | |
| Stock-based compensation | 8.1 | 5.4 | 6.6 | 2.5 | 2.1 | | 0.0 | 0.5 |
| Deferred taxes | | | | | | | | 0.1 |
| Change in working capital [+] | 10.4 | -50.2 | -17.5 | 18.3 | 22.4 | -6.9 | -2.1 | 0.1 |
| Restricted cash | | | | -0.3 | -1.1 | | | |
| Accounts receivable | 12.0 | -18.7 | 5.4 | 5.0 | 0.6 | -10.0 | 0.6 | -1.4 |
| Deferred revenues | | | | | 1.6 | | 2.1 | 0.6 |
| Other | -1.6 | -31.5 | -22.9 | 13.6 | 21.3 | | | |
| Other operating activities | -107.9 | -2.1 | 8.0 | | | | | |
| Cash from operations | 290.3 | 229.3 | 37.4 | 32.8 | 29.4 | 2.6 | 58.8 | 39.6 |
| |
| Capital expenditures | -83.7 | -43.4 | -4.6 | -16.5 | -8.3 | 0.0 | -9.8 | -1.8 |
| Purchases of property and equipment | -83.7 | -43.4 | -4.6 | -16.5 | -8.3 | | -9.8 | -1.8 |
| Acquisitions | | | | -3.7 | | -78.8 | | |
| Other cash from investing | -740.7 | 133.0 | -828.2 | -451.0 | -207.7 | | -323.4 | -679.3 |
| Cash from investing | -824.5 | 89.5 | -832.8 | -471.2 | -216.1 | -78.8 | -333.2 | -681.1 |
| |
| Cash dividends paid | -224.5 | -148.5 | -54.9 | -10.8 | | | -60.2 | -41.2 |
| Issuance of common stock, net | 410.8 | 0.0 | 289.9 | 627.2 | 45.5 | | 547.7 | 537.6 |
| Financing costs | -18.6 | -6.9 | -31.8 | -36.8 | -3.5 | | -2.5 | -5.2 |
| Other cash from financing | 291.8 | -251.4 | 482.1 | -58.1 | 75.5 | | -25.5 | 75.7 |
| Cash from financing | 496.7 | -393.0 | 748.9 | 595.2 | 124.6 | 75.7 | 464.5 | 577.2 |
| |
| Free cash flow | 206.6 | 185.8 | 32.8 | 16.3 | 21.1 | 2.6 | 49.0 | 37.7 |
| Per share (diluted) | $1.37 | $1.32 | $0.54 | $0.57 | $0.43 | | $0.25 | $0.28 |