Utility Regulatory Assets and Liabilities and Regulatory Matters - Regulatory Assets and Liabilities Associated with Utilities (Details) - USD ($) $ in Millions		Sep. 30, 2015	Sep. 30, 2014
Regulatory Assets and Liabilities
Regulatory assets	[1]	$ 304.2	$ 268.2
Regulatory liabilities	[1]	71.0	32.5
Postretirement Benefits
Regulatory Assets and Liabilities
Regulatory liabilities	[1]	20.0	18.6
Environmental Overcollections
Regulatory Assets and Liabilities
Regulatory liabilities	[1]		0.3
Deferred Fuel and Power Refunds
Regulatory Assets and Liabilities
Regulatory liabilities	[1]	36.6	0.3
State Tax Benefits — Distribution System Repairs
Regulatory Assets and Liabilities
Regulatory liabilities	[1]	13.3	10.1
Other
Regulatory Assets and Liabilities
Regulatory liabilities	[1]	1.1	3.2
Income Taxes Recoverable
Regulatory Assets and Liabilities
Regulatory assets	[1]	115.9	110.7
Underfunded Pension and Postretirement Plans
Regulatory Assets and Liabilities
Regulatory assets	[1]	140.8	110.1
Environmental Costs
Regulatory Assets and Liabilities
Regulatory assets	[1]	20.0	14.6
Deferred Fuel and Power Costs
Regulatory Assets and Liabilities
Regulatory assets	[1]		11.8
Removal Costs, Net
Regulatory Assets and Liabilities
Regulatory assets	[1]	21.2	16.8
Other
Regulatory Assets and Liabilities
Regulatory assets	[1]	$ 6.3	$ 4.2

[1] Regulatory liabilities are recorded in other current and other noncurrent liabilities in the Consolidated Balance Sheets.