Restatements of Condensed Consolidated Financial Statements - Condensed Consolidated Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Mar. 31, 2013
Assets:
Deferred income taxes	$ 10.8		$ 10.6	$ 14.9
Prepaid expenses and other current assets	48.5		57.1	53.5
Property, plant and equipment	4,519.1		4,480.2	4,285.4
Liabilities and equity:
Other current liabilities	668.6		627.5	642.8
Deferred income taxes	984.4		962.3	918.7
Other noncurrent liabilities	526.0		527.2	615.7
Retained earnings	1,579.9		1,308.3	1,378.0
Accumulated other comprehensive loss	24.3	32.2	8.4	(46.5)
Noncontrolling interests	1,206.9		1,055.4	1,231.1
As Previously Reported
Assets:
Deferred income taxes				35.9
Prepaid expenses and other current assets				52.1
Property, plant and equipment				4,286.7
Liabilities and equity:
Other current liabilities				644.2
Deferred income taxes				941.4
Other noncurrent liabilities				614.0
Retained earnings				1,379.4
Accumulated other comprehensive loss				(45.6)
Noncontrolling interests				1,227.3
Adjustment
Assets:
Deferred income taxes				(21.0)
Prepaid expenses and other current assets				1.4
Property, plant and equipment				(1.3)
Liabilities and equity:
Other current liabilities				(1.4)
Deferred income taxes				(22.7)
Other noncurrent liabilities				1.7
Retained earnings				(1.4)
Accumulated other comprehensive loss				(0.9)
Noncontrolling interests				$ 3.8