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Property, Plant and Equipment - Capitalized Costs of Unproved Properties Excluded from Amortization (Parenthetical) (Details) (USD $) In Millions, unless otherwise specified		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Year Cost Incurred 2012	Dec. 31, 2011 Year Cost Incurred 2011	Dec. 31, 2010 Year Cost Incurred 2010	Dec. 31, 2009 Year Cost Incurred 2009 and Prior
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Pipe inventory costs, cumulative	$ 72.4				$ 10.1
Pipe inventory costs, period costs		$ 54.9	$ 2.3	$ 5.1