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	3 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Dec. 31, 2012	Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Document Period End Date	Dec. 31, 2013
Cash and cash equivalents	$ 1,293.8		$ 1,899.7		$ 1,103.7	$ 1,470.7
Derivatives	294.5		221.8
Equity conversion feature of preferred stock	378.0		330.8
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		[1]		[1]
Contingent purchase price reduction receivable	41.5		41.0
Assets, Fair Value Disclosure, Recurring	709.5		523.5
Equity conversion feature of preferred stock	378.0		330.8
Liabilities, Fair Value Disclosure, Recurring	2,172.6		1,875.2
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,293.8	[1]	1,899.7	[1]
Contingent purchase price reduction receivable
Assets, Fair Value Disclosure, Recurring			2,761.4
Equity conversion feature of preferred stock
Liabilities, Fair Value Disclosure, Recurring	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		[1]	0	[1]
Contingent purchase price reduction receivable
Assets, Fair Value Disclosure, Recurring			14,536.0
Equity conversion feature of preferred stock
Liabilities, Fair Value Disclosure, Recurring	11.3		13.4
Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,293.8	[1]	1,899.7	[1]
Contingent purchase price reduction receivable	41.5		41.0
Assets, Fair Value Disclosure, Recurring	18,258.3		17,820.9
Equity conversion feature of preferred stock	378.0		330.8
Liabilities, Fair Value Disclosure, Recurring	2,183.9		1,888.6
Fixed Index Annuity [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	1,644.7		1,544.4
Fixed Index Annuity [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability
Fixed Index Annuity [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability
Fixed Index Annuity [Member] | Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	1,644.7		1,544.4
Front Street Future Policyholder Benefits Reserve [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	149.9
Front Street Future Policyholder Benefits Reserve [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability
Front Street Future Policyholder Benefits Reserve [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability
Front Street Future Policyholder Benefits Reserve [Member] | Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	$ 149.9

[1] (a)The fair values of cash equivalents and equity investments set forth above are generally based on quoted or observed market prices.