Fair Value of Financial Instruments Fair Value of Financial Instruments - Assets and Liabilities Carrying at Fair Value Measured on a Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Jun. 30, 2014		Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Document Period End Date	Jun. 30, 2014
Cash and cash equivalents	$ 1,455.9		$ 1,899.7	$ 1,243.7	$ 1,470.7
Derivatives	324.7		221.8
Equity conversion feature of preferred stock			330.8
Asset-backed loans	724.3		560.4
Other Invested Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - trading	174.3		31.2
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset-backed loans	724.3
Total financial assets	884.9
Total debt	5,303.4	[1]
Liabilities Related to Investment Contracts, Fair Value Disclosure	14,353.4
Financial Liabilities Fair Value Disclosure	19,656.8
Reported Value Measurement [Member] | Policy loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Policy loans and other invested assets	$ 160.6

[1] (a)