| In millions, except per share items | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Net income | -464.5 | -435.0 | -1,522.2 | 232.9 | 191.4 | 281.4 | 412.5 | 510.9 |
| Depreciation and amortization [+] | 74.4 | 105.6 | 170.5 | 216.7 | 225.3 | 225.9 | 189.7 | 192.6 |
| Depreciation | 73.2 | 102.5 | 154.6 | 197.6 | 206.1 | 211.1 | 188.7 | 191.7 |
| Amortization of intangible assets | 1.2 | 3.1 | 15.9 | 19.1 | 19.2 | 14.8 | 1.0 | 0.9 |
| Asset impairment charges | 290.1 | 443.3 | 383.0 | | | | | |
| Stock-based compensation | 32.0 | 21.9 | 36.1 | 43.0 | 40.7 | 40.1 | 61.1 | 48.2 |
| Tax benefit from stock-based compensation | | | | | | | | -4.1 |
| Deferred taxes | 28.6 | -20.3 | 320.6 | 60.7 | 100.3 | -7.9 | 4.7 | 62.1 |
| Change in working capital [+] | 9.0 | -415.0 | 463.6 | 219.2 | -316.8 | 534.9 | -319.2 | 118.5 |
| Accounts receivable | -5.4 | -138.4 | -210.4 | 40.6 | -162.7 | 337.8 | -190.1 | 336.1 |
| Accounts payable | 6.4 | -343.1 | -46.9 | 176.3 | -137.4 | 200.5 | -57.3 | -153.5 |
| Other | 8.0 | 66.5 | 720.9 | 2.3 | -16.7 | -3.4 | -71.7 | -64.0 |
| Other operating activities | 55.9 | 485.5 | 367.4 | -610.3 | 361.1 | -368.4 | 500.4 | |
| Cash from operations | 25.3 | 185.9 | 219.0 | 162.2 | 602.0 | 705.9 | 849.1 | 642.6 |
| |
| Capital expenditures [+] | -75.1 | -113.4 | -180.8 | -211.0 | -283.1 | -235.9 | -240.2 | -324.7 |
| Purchases of property and equipment | -75.1 | -113.4 | -180.8 | -211.0 | -283.1 | -235.9 | -240.2 | -324.7 |
| Sales of property and equipment | 145.7 | 111.6 | 66.0 | 81.0 | 96.1 | 81.2 | 94.3 | 105.9 |
| Acquisitions | | | | | | -240.7 | | |
| Sales of short-term investments, net [+] | -103.8 | -15.4 | 207.4 | 57.6 | -20.9 | 162.1 | 25.4 | 8.9 |
| Purchases of short-term investments | -148.5 | -35.1 | -31.2 | -483.5 | -237.4 | -360.0 | -386.0 | -410.5 |
| Sales of short-term investments | 44.7 | 19.6 | 238.5 | 541.1 | 216.4 | 522.1 | 411.4 | 419.4 |
| Other cash from investing | -88.7 | -24.3 | -12.0 | 73.8 | -276.3 | -508.0 | 54.0 | 10.8 |
| Cash from investing | -121.9 | -41.6 | 80.5 | 1.4 | -484.3 | -741.4 | -66.5 | -199.1 |
| |
| Cash dividends paid | | | | -118.7 | -118.0 | -118.0 | -125.2 | -126.2 |
| Repurchase of common stock, net | | | | -50.0 | | -9.7 | -509.7 | -906.1 |
| Option exercises | | | | 7.3 | 9.4 | 3.7 | 1.8 | 24.2 |
| Financing costs | | | | -5.1 | | -3.5 | | -7.7 |
| Other cash from financing | 122.3 | 48.4 | -77.3 | 30.5 | -88.1 | 117.5 | -91.6 | 382.4 |
| Cash from financing | 122.3 | 48.4 | -77.3 | -140.5 | -215.5 | -10.4 | -728.2 | -666.4 |
| |
| Free cash flow | -49.7 | 72.4 | 38.2 | -48.8 | 318.9 | 470.0 | 608.9 | 317.9 |
| Per share (diluted) | ($0.35) | $0.52 | $0.27 | ($0.35) | $2.26 | $3.34 | $4.15 | $1.99 |