Loans Held for Sale - Additional Information (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	$ 612,000,000	$ 230,000,000
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	528,000,000	76,000,000
Valuation allowance	11,000,000	0
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	84,000,000	154,000,000
Valuation allowance	15,000,000	77,000,000
Commercial Loans - Fair Value Option [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	152,000,000	58,000,000
Global Banking [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	276,000,000
Commercial Real Estate [Member] | Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	100,000,000	18,000,000
Subprime Residential Mortgage Loans [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for sale	$ 4,000,000	$ 46,000,000