Restatements of Condensed Consolidated Financial Statements - Condensed Consolidated Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Net (loss) income	$ 592.6	$ 486.7
Depreciation and amortization	271.7	269.2
Deferred income taxes, net	21.2	32.2
Net change in realized gains and losses deferred as cash flow hedges		0
Unrealized losses on derivative instruments	3.1	(0.7)
Other, net	(4.9)	(3.6)
Accounts receivable and accrued utility revenues	(56.4)	(146.2)
Inventories	34.8	51.3
Accounts payable	(40.8)	(25.5)
Other current liabilities	5.0	(73.8)
As Previously Reported
Net (loss) income		481.8
Depreciation and amortization		266.3
Deferred income taxes, net		35.5
Net change in realized gains and losses deferred as cash flow hedges		5.0
Unrealized losses on derivative instruments		0
Other, net		(11.3)
Accounts receivable and accrued utility revenues		(141.1)
Inventories		54.1
Accounts payable		(26.9)
Other current liabilities		(73.8)
Adjustment
Net (loss) income		4.9
Depreciation and amortization		2.9
Deferred income taxes, net		(3.3)
Net change in realized gains and losses deferred as cash flow hedges		(5.0)
Unrealized losses on derivative instruments		(0.7)
Other, net		7.7
Accounts receivable and accrued utility revenues		(5.1)
Inventories		(2.8)
Accounts payable		1.4
Other current liabilities		$ 0