INCOME TAXES - Significant Items in Net Deferred Tax Liability (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Deferred tax assets:
Deferred tax assets, Current	$ 2.7	$ 21.6
Deferred tax assets, Noncurrent	281.8	0
Deferred tax liabilities:
Deferred tax liabilities, Current	0.4	1.6
Deferred tax liabilities, Noncurrent	4.0	205.6
Deferred Tax Assets, Net, Current	2.3	20.0
Deferred Tax Assets, Net, Noncurrent	277.8	0
Deferred Tax Liabilities, Net, Noncurrent	0	(205.6)
Deferred tax assets, Current
Deferred tax assets:
Unbilled and deferred revenue	2.5	12.5
Allowance for doubtful accounts	0	1.8
Insurance accruals	0	1.8
Compensation accruals	0	2.5
Inventories	0	1.3
Gas supply adjustment related accruals	0	0.7
Pension and other costs	0	0
Goodwill	0	0
Net operating loss	0	0
Other	0.2	1.0
Deferred tax assets, Noncurrent
Deferred tax assets:
Unbilled and deferred revenue	0	0
Allowance for doubtful accounts	0	0
Insurance accruals	0	0
Compensation accruals	0	0
Inventories	0	0
Gas supply adjustment related accruals	0	0
Pension and other costs	10.6	0
Goodwill	266.1	0
Net operating loss	5.1	0
Other	0	0
Deferred tax liabilities, Current
Deferred tax liabilities:
Depreciation and basis differences	0	0
Pension and other costs	0	0
Other	0.4	1.6
Deferred tax liabilities, Noncurrent
Deferred tax liabilities:
Depreciation and basis differences	4.0	186.6
Pension and other costs	0	19.0
Other	$ 0	$ 0