Investments - Cash Flows from Consolidated Investing Activities by Security (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Gain (Loss) on Investments [Line Items]
Document Period End Date	Dec. 31, 2013
Proceeds from investments sold, matured or repaid	$ 1,820.3	$ 3,054.7
Cost of investments acquired	(2,728.2)	(3,440.4)
Available-for-sale Securities [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from investments sold, matured or repaid		2,913.4
Cost of investments acquired	(2,598.5)	(3,395.1)
Trading (acquired for holding) [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from investments sold, matured or repaid		91.0
Cost of investments acquired	(4.4)
Derivative and other [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from investments sold, matured or repaid	114.4	50.3
Cost of investments acquired	$ (125.3)	$ (45.3)