Formation of a Master Limited Partnership Variable Interest Entity (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Formation of a Master Limited Partnership [Abstract]
Cash	$ 106.2	$ 0
Receivables	29.2	27.4
Inventories	58.7	63.2
Properties, plants and equipment, net	766.8	768.7
Deferred income taxes	0	21.4
Deferred charges and other assets	8.6	4.8
Total assets	969.5	885.5
Accounts payable	51.0	41.5
Payable to affiliate	3.1	17.0
Accrued liabilities	2.1	0
Interest payable	2.4	0
Long-term debt	149.7	225.0
Deferred income taxes	1.4	0
Other deferred credits and liabilities	0.3	0.3
Total equity	759.5	601.7
Total liabilities and parent net equity	$ 969.5	$ 885.5