Revisions and Restatements of Consolidated Financial Statements - Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Net income	$ 427.6	$ 197.7	$ 320.0
Depreciation, Depletion and Amortization	363.1	315.0	227.7
Deferred Income Tax Expense (Benefit)	48.7	90.2	91.5
Net change in realized gains and losses deferred as cash flow hedges
Unrealized gains on derivative instruments	(0.2)	(17.2)	(19.6)
Other, net	(41.4)	(11.0)	4.3
As Previously Reported
Net income		186.6	308.2
Depreciation, Depletion and Amortization		316.0	227.9
Deferred Income Tax Expense (Benefit)		82.9	82.7
Net change in realized gains and losses deferred as cash flow hedges		(6.6)	12.2
Unrealized gains on derivative instruments		0	0
Other, net		(10.7)	(7.1)
Adjustment
Net income		11.1	11.8
Depreciation, Depletion and Amortization		(1.0)	(0.2)
Deferred Income Tax Expense (Benefit)		7.3	8.8
Net change in realized gains and losses deferred as cash flow hedges		6.6	(12.2)
Unrealized gains on derivative instruments		(17.2)	(19.6)
Other, net			11.4
Classification correction excluded [Member]
Other, net		(17.5)
Classification correction excluded [Member] | Adjustment
Other, net		$ (6.8)