Income Taxes - Significant Components of our deferred tax assets & liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Accrued postretirement benefit cost	$ 29.5	$ 38.9
Net operating losses and tax credits	453.1	430.3
Disallowed interest expense	17.8	6.9
Foreign basis differences	0.0	16.2
Derivative and hedging contracts	18.6	0.5
Other	13.9	12.3
Total deferred tax assets	532.9	505.1
Valuation allowance	(485.8)	(499.4)
Net deferred tax assets	47.1	5.7
Deferred tax liabilities:
Tax over financial statement depreciation	(86.2)	(95.0)
Foreign basis differences	(19.6)	0.0
Total deferred tax liabilities	(105.8)	(95.0)
Net deferred tax liability	$ (58.7)	$ (89.3)

The amount as of the balance sheet date of the estimated future tax effects attributable to the difference between the tax basis and the basis in accordance with generally accepted accounting principles of foreign basis differences which will decrease future taxable income when such basis difference reverses.

No definition available.