Acquisition of Totalgaz - Schedule of Preliminary Purchase Price Allocation (Details) - USD ($) $ in Millions		Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	[1]	May 29, 2015
Liabilities assumed:
Goodwill		$ 2,981.3	$ 2,953.4	$ 2,927.7
Totalgaz SAS
Assets acquired:
Cash						$ 86.8
Accounts receivable	[2]					170.3
Prepaid expenses and other current assets						11.0
Property, plant and equipment						375.6
Intangible assets	[3]					91.3
Other assets						21.4
Total assets acquired						756.4
Liabilities assumed:
Accounts payable						109.2
Other current liabilities						103.5
Deferred income taxes						117.5
Other noncurrent liabilities						113.4
Total liabilities assumed						443.6
Goodwill						183.8
Net consideration transferred (including working capital adjustments)						496.6
Indefinite-lived intangible assets acquired	[3]					12.0
Totalgaz SAS | Customer Relationships
Liabilities assumed:
Finite-lived intangibles assets acquired	[3]					$ 79.3

[1] Certain amounts have been restated to reflect the current-year changes in our segment presentation as described above.

[2] Approximates the gross contractual amounts of receivables acquired.

[3] Comprises $79.3 of customer relationships and $12.0 of tradenames.