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| 14. VALUATION AND QUALIFYING ACCOUNTS |
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| The following table summarizes the activity and ending balances in our allowance for doubtful accounts and estimated revenue adjustments (amounts in millions): |
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| Allowance for Doubtful Accounts |
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| | Year End | | Balance at Beginning of Year | | Provision for Doubtful Accounts (1) | | Write-Offs | | Balance at End of Year | |
| | 2015 | | $ | 14.3 | | $ | 14.1 | | $ | (11.9) | | $ | 16.5 | |
| | 2014 | | | 14.2 | | | 16.4 | | | (16.3) | | | 14.3 | |
| | 2013 | | | 21.0 | | | 16.4 | | | (23.2) | | | 14.2 | |
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| | (1) Includes $0.1 million and $0.6 million from discontinued operations for the years ended December 31, 2014 and 2013, respectively. | |
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| Estimated Revenue Adjustments |
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| | Year End | | Balance at Beginning of Year | | Provision for Estimated Revenue Adjustments (1) | | Write-Offs | | Balance at End of Year | |
| | 2015 | | $ | 3.1 | | $ | 6.1 | | $ | (5.2) | | $ | 4.0 | |
| | 2014 | | | 3.9 | | | 5.1 | | | (5.9) | | | 3.1 | |
| | 2013 | | | 6.4 | | | 9.4 | | | (11.9) | | | 3.9 | |
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| | (1) Includes $0.1 million and $0.4 million from discontinued operations for the years ended December 31, 2014 and 2013, respectively. | |