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Income Taxes - Significant Components of our deferred tax assets & liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Deferred tax assets: |  |
Accrued postretirement benefit cost | $ 39.3 | $ 40.3
Accrued liabilities | 10.8 | 10.9
Share-based compensation | 0.9 | 2.1
Goodwill | 0.0 | 0.4
Net operating losses and tax credits | 432.8 | 482.8
Foreign basis differences | 15.0 | 13.5
Ravenswood retiree legal settlement | 1.9 | 2.4
Other | 2.8 | 1.9
Total deferred tax assets | 503.5 | 554.3
Valuation allowance | (492.4) | (552.5)
Net deferred tax assets | 11.1 | 1.8
Deferred tax liabilities: |  |
Derivatives | (3.5) | 0.0
Tax over financial statement depreciation | (102.4) | (103.9)
Total deferred tax liabilities | (105.9) | (103.9)
Net deferred tax liability | $ (94.8) | $ (102.1)

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