Income Tax Matters, Components of Deferred Tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Deferred income tax assets:
Loss and credit carryforwards	$ 342.2		$ 375.6
VEBAs	7.6		0
Other assets	35.3		39.6
Inventories and other	1.7		8.3
Valuation allowances	(18.7)		(18.8)
Total deferred income tax assets	368.1		404.7
Deferred income tax liabilities:
Property, plant and equipment	(69.7)		(67.2)
VEBAs	(136.9)		(47.6)
Total deferred income tax liabilities	(206.6)		(114.8)
Net deferred income tax assets	161.5	[1]	289.9	[2]
Net deferred income tax assets, current	59.5		63.0
Net deferred income tax assets, long term	$ 102.0		$ 226.9

[1] Of the total net deferred income tax assets of $161.5, $59.5 was included in Prepaid expenses and other current assets and $102.0 was presented as Deferred tax assets, net on the Consolidated Balance Sheet as of December 31, 2012.

[2] Of the total net deferred income tax assets of $289.9, $63.0 was included in Prepaid expenses and other current assets and $226.9 was presented as Deferred tax assets, net on the Consolidated Balance Sheet as of December 31, 2011.