ACQUISITIONS - Preliminary Fair Value of Alagasco Assets Acquired and Liabilities Assumed (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Aug. 31, 2014 Alagasco	Sep. 30, 2013 Alagasco	Sep. 01, 2013 Alagasco
Assets:
Utility plant			$ 892.7
Accounts receivable and other current assets			37.3
Inventories			47.7
Prepayments and other			26.6
Total Current Assets			1,004.3
Regulatory assets			99.5
Deferred tax asset			278.4
Pension and other postretirement			25.7
Other			18.2
Total Deferred Charges			421.8
Total Assets Acquired			1,426.1
Liabilities:
Accounts payable			32.9
Customer deposits			19.9
Taxes accrued			28.4
Regulatory liabilities
Current portion of long-term debt			15.0
Other			92.2
Total Current Liabilities			188.4
Pension and postretirement benefit costs			27.9
Asset retirement obligations			30.6
Regulatory liabilities			56.1
Long-term debt			249.8
Other			15.8
Total Deferred Credits and Other Liabilities			380.2
Total Liabilities Assumed			568.6
Goodwill	937.8	247.1	727.6	0	727.6
Deferred Tax Elimination			(267.8)
Net Assets Acquired			$ 1,317.3