Derivatives (Net Gains (Losses) Recorded in the Consolidated Statements of Income Relating to Free-Standing Derivative Instruments Used for Risk Management and Other Business Purposes) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
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Derivative Instruments, Gain (Loss)
Proceeds From Warrant Exercises	$ 9	$ 89