The following tables summarize the Company's unrealized gains and losses and fair value of investments designated as available-for-sale and trading securities as of December 31, 2016 and December 31, 2015 (in millions): | | | | | | | | | | | | | | | | | | Amortized Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Estimated Fair Value | As of December 31, 2016 | | | | | | | | Fixed income securities: | | | | | | | | Asset-backed securities | $ | 303.0 |
| | $ | 0.2 |
| | $ | (0.2 | ) | | $ | 303.0 |
| Certificates of deposit | 66.1 |
| | — |
| | — |
| | 66.1 |
| Commercial paper | 147.7 |
| | — |
| | — |
| | 147.7 |
| Corporate debt securities | 846.5 |
| | 0.4 |
| | (2.0 | ) | | 844.9 |
| Foreign government debt securities | 34.0 |
| | — |
| | (0.1 | ) | | 33.9 |
| Time deposits | 264.6 |
| | — |
| | — |
| | 264.6 |
| U.S. government agency securities | 127.0 |
| | — |
| | (0.3 | ) | | 126.7 |
| U.S. government securities | 390.7 |
| | 0.1 |
| | (0.4 | ) | | 390.4 |
| Total fixed income securities | 2,179.6 |
| | 0.7 |
| | (3.0 | ) | | 2,177.3 |
| Money market funds | 592.2 |
| | — |
| | — |
| | 592.2 |
| Mutual funds | 8.0 |
| | — |
| | — |
| | 8.0 |
| Publicly-traded equity securities | 5.3 |
| | — |
| | (0.7 | ) | | 4.6 |
| Total available-for-sale securities | 2,785.1 |
| | 0.7 |
| | (3.7 | ) | | 2,782.1 |
| Trading securities in mutual funds(1) | 21.0 |
| | — |
| | — |
| | 21.0 |
| Total | $ | 2,806.1 |
| | $ | 0.7 |
| | $ | (3.7 | ) | | $ | 2,803.1 |
| | | | | | | | | Reported as: | | | | | | | | Cash equivalents | $ | 907.1 |
| | $ | — |
| | $ | — |
| | $ | 907.1 |
| Restricted investments(2) | 71.9 |
| | — |
| | — |
| | 71.9 |
| Short-term investments | 753.4 |
| | 0.1 |
| | (1.2 | ) | | 752.3 |
| Long-term investments | 1,073.7 |
| | 0.6 |
| | (2.5 | ) | | 1,071.8 |
| Total | $ | 2,806.1 |
| | $ | 0.7 |
| | $ | (3.7 | ) | | $ | 2,803.1 |
|
________________________________ | | (1) | Balance includes the Company's non-qualified deferred compensation plan assets. |
| | (2) | Includes $4.0 million of short-term restricted investments classified as prepaid expenses and other current assets on the Consolidated Balance Sheets. |
| | | | | | | | | | | | | | | | | | Amortized Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Estimated Fair Value | As of December 31, 2015 | | | | | | | | Fixed income securities: | | | | | | | | Asset-backed securities | $ | 312.2 |
| | $ | — |
| | $ | (0.5 | ) | | $ | 311.7 |
| Certificates of deposit | 9.6 |
| | — |
| | — |
| | 9.6 |
| Commercial paper | 17.7 |
| | — |
| | — |
| | 17.7 |
| Corporate debt securities | 913.8 |
| | 0.2 |
| | (2.6 | ) | | 911.4 |
| Foreign government debt securities | 16.5 |
| | — |
| | — |
| | 16.5 |
| Time deposits | 140.0 |
| | — |
| | — |
| | 140.0 |
| U.S. government agency securities | 204.1 |
| | — |
| | (0.4 | ) | | 203.7 |
| U.S. government securities | 278.0 |
| | — |
| | (0.4 | ) | | 277.6 |
| Total fixed income securities | 1,891.9 |
| | 0.2 |
| | (3.9 | ) | | 1,888.2 |
| Money market funds | 29.7 |
| | — |
| | — |
| | 29.7 |
| Mutual funds | 6.1 |
| | 0.1 |
| | — |
| | 6.2 |
| Publicly-traded equity securities | 8.7 |
| | 0.8 |
| | (0.7 | ) | | 8.8 |
| Total available-for-sale securities | 1,936.4 |
| | 1.1 |
| | (4.6 | ) | | 1,932.9 |
| Trading securities in mutual funds(1) | 17.7 |
| | — |
| | — |
| | 17.7 |
| Total | $ | 1,954.1 |
| | $ | 1.1 |
| | $ | (4.6 | ) | | $ | 1,950.6 |
| | | | | | | | | Reported as: | | | | | | | | Cash equivalents | $ | 143.4 |
| | $ | — |
| | $ | — |
| | $ | 143.4 |
| Restricted investments | 35.8 |
| | 0.1 |
| | — |
| | 35.9 |
| Short-term investments | 527.2 |
| | 0.9 |
| | (1.0 | ) | | 527.1 |
| Long-term investments | 1,247.7 |
| | 0.1 |
| | (3.6 | ) | | 1,244.2 |
| Total | $ | 1,954.1 |
| | $ | 1.1 |
| | $ | (4.6 | ) | | $ | 1,950.6 |
|
_______________________________ | | (1) | Balance includes the Company's non-qualified deferred compensation plan assets. |
|