DERIVATIVE FINANCIAL INSTRUMENTS (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2016 USD ($) designated_hedge	Mar. 31, 2015 USD ($)	Mar. 31, 2016 USD ($) designated_hedge	Mar. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)
Derivative [Line Items]
Receivable for uncollectible derivative transaction fee revenues	$ 7,000,000		$ 7,000,000		$ 7,000,000
Maximum loss exposure on interest rate derivatives	52,000,000		52,000,000
Maximum loss exposure under forward foreign exchange contracts	200,000		200,000
Derivative asset position
Derivative [Line Items]
Cash collateral included in net fair value of all open derivative positions, aggregate net liability	59,000,000		59,000,000		44,000,000
Derivative liability position
Derivative [Line Items]
Cash collateral included in the net fair value of all open derivative liability positions, aggregate net asset	26,000,000		26,000,000		$ 26,000,000
Forward foreign exchange contracts
Derivative [Line Items]
Hedge ineffectiveness	0	$ 0	0	$ 0
Gain (loss) from components excluded from assessment of fair value hedge effectiveness	$ 0	$ 0	$ 0	$ 0
OTC derivatives
Derivative [Line Items]
Number of designated as fair value hedges | designated_hedge	0		0
Number of derivatives designated as cash flow hedges | designated_hedge	0		0
Derivative instruments associated with offsetting matched book positions
Derivative [Line Items]
Number of designated as fair value hedges | designated_hedge	0		0
Number of derivatives designated as cash flow hedges | designated_hedge	0		0
Interest rate contract
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months			$ (6,100,000)
Maximum length of time hedged in cash flow hedge			10 years