Schedule II - Condensed Financial Information of Registrant - Condensed Balance Sheet of Registrant (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
ASSETS
Cash and cash equivalents	$ 270.1	$ 465.2	$ 643.2	$ 673.6
Receivables, net	285.7	269.4
Assets, Current	30,036.1	1,823.7
Cash and cash equivalents	2,631.7	2,405.3
Property, plant and equipment, net (Note 10)	503.9	367.4
Total assets	35,849.7	33,580.1
LIABILITIES AND EQUITY
Accounts Payable, Current	373.1	316.0
Interest Payable, Current	78.0	68.3
Liabilities, Current	27,645.0	1,241.2
Long-term debt	5,801.9	5,575.4
Employee benefit obligations	97.2	104.9	87.8
Deferred tax liabilities (Note 18)	493.2	512.1
Other liabilities	26.2	26.0
Total liabilities	33,902.8	31,762.9
Stockholders’ equity:
Common stock, $0.01 par; 500,000.0 thousand shares authorized; 200,624.9 thousand and 200,789.1 thousand shares issued and outstanding at September 30, 2017 and 2016, respectively.	2.0	2.0
Accumulated deficit	(925.9)	(1,031.9)
Accumulated other comprehensive income	309.0	220.9	(40.7)
Total permanent equity	1,946.9	1,817.2	1,588.1	2,257.0
Total liabilities and equity	35,849.7	33,580.1
Parent Company [Member]
ASSETS
Cash and cash equivalents	92.9	170.9	$ 297.2	$ 420.0
Receivables, net	0.0	0.1
Assets, Current	92.9	171.0
Cash and cash equivalents	2,423.9	1,870.1
Advances to consolidated subsidiaries	0.2	9.6
Deferred Tax Assets, Net, Current	0.0	351.2
Property, plant and equipment, net (Note 10)	0.8	1.1
Deferred charges and other assets	0.5	0.6
Total assets	2,518.3	2,403.6
LIABILITIES AND EQUITY
Accounts Payable, Current	0.8	0.2
Accrued Liabilities, Current	36.1	48.2
Liabilities, Current	36.9	48.4
Long-term debt	1,718.3	1,711.2
Employee benefit obligations	4.2	5.2
Other liabilities	0.9	0.7
Total liabilities	1,760.3	1,765.5
Stockholders’ equity:
Common stock, $0.01 par; 500,000.0 thousand shares authorized; 200,624.9 thousand and 200,789.1 thousand shares issued and outstanding at September 30, 2017 and 2016, respectively.	2.0	2.0
Additional paid-in capital	1,372.9	1,447.1
Accumulated deficit	(925.9)	(1,031.9)
Accumulated other comprehensive income	309.0	220.9
Total permanent equity	758.0	638.1
Total liabilities and equity	$ 2,518.3	$ 2,403.6

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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- Definition

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).