Fair Value Measurements (Schedule of Equity Method Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Schedule of Equity Method Investments [Line Items]
Revenue	$ 1,018	$ 239	$ 148
Net investment income (a)	1,620	161	88
Net income	196	216	$ 135
Total assets	21,101	25,497
Total liabilities	19,348	24,209
Non-controlling interests	12	$ 14
Alexander Forbes Group Holdings Limited
Schedule of Equity Method Investments [Line Items]
Net investment income (a)	$ 1,500