Loans Held for Sale - Additional Information (Details) - USD ($)	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	$ 2,185,000,000	$ 612,000,000
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	2,095,000,000	528,000,000
Valuation allowance	21,000,000	5,000,000
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	90,000,000	84,000,000
Valuation allowance	13,000,000	15,000,000
Commercial Loans - Fair Value Option [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	151,000,000	384,000,000
Global Banking [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	200,000,000	428,000,000
Commercial Real Estate [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	1,895,000,000	100,000,000
Transfer of loans to held-for-sale	1,889,000,000
Lower of amortized cost or fair value adjustment	0
Subprime [Member] | Residential Portfolio Segment [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	$ 3,000,000	$ 4,000,000