Fair Value Measurements (Schedule of Equity Method Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Schedule of Equity Method Investments [Line Items]
Revenue		$ 843	$ 1,018	$ 239
Net investment income	[1]	1,824	1,620	161
Net income		91	196	$ 216
Total assets		22,997	21,101
Total liabilities		21,087	19,348
Non-controlling interests		12	12
Alexander Forbes Group Holdings Limited
Schedule of Equity Method Investments [Line Items]
Net investment income		$ 1,900	$ 1,500

[1] (a) Net investment income in 2016 and 2015 includes approximately $1.9 billion and $1.5 billion, respectively, related to Alexander Forbes, substantially all of which is credited to policy holders.