Subsequent Events Subsequent Events - Divestitures (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016		Sep. 30, 2015
Subsequent Event [Line Items]
Cash and cash equivalents	$ 348.8	$ 566.5	$ 497.3		$ 661.2
Receivables, net	556.5		556.3
Other assets	157.2		172.6
Assets	35,662.7		35,792.8
Debt	5,459.0		5,430.9	[1],[2]
Accounts payable and other current liabilities	900.4		989.8
Other liabilities	26.7		32.0
Liabilities	33,993.3		33,975.6
Stockholders' Equity Attributable to Parent	548.1		638.1
Noncontrolling interest	$ 1,121.3		$ 1,179.1
Document Fiscal Year Focus	2017
Operating income	$ 117.7	99.8
Interest Expense	91.7	95.2
Other income (expense), net	1.4	(0.7)
Net income	260.8	7.0
Less: Net income attributable to noncontrolling interest	48.6	40.9
Net Income (Loss) Attributable to Parent	212.2	(33.9)
Compass Production Partners G.P. [Member]
Subsequent Event [Line Items]
Operating income		(64.5)
Interest Expense		2.3
Gain (Loss) on Disposition of Oil and Gas Property		105.6
Other income (expense), net		1.8
Net income	$ 0.0	$ 33.1

[1] The carrying value of cash and cash equivalents, trade receivables, accounts payable and accrued investment income approximate fair value due to their short duration and, accordingly, they are not presented in the tables above.

[2] The fair value of debt set forth above is generally based on quoted or observed market prices.