Capitalized Servicing Assets - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Servicing Assets at Fair Value [Line Items]
Residential mortgage loans securitized formerly held in Company's portfolio		$ 1,300,000,000
Automobile loans securitized and sold	0	1,400,000,000
Residential Mortgage Loans [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	64,400,000,000	69,100,000,000	64,400,000,000	69,100,000,000	32,100,000,000
Estimated fair value of capitalized mortgage loan servicing assets	228,000,000	266,000,000	228,000,000	266,000,000
Weighted average discount rates used to estimate fair value of capitalized mortgaged loan servicing assets			11.90%	9.30%
Weighted-average option-adjusted spread in the discount rate			1065 basis points	770 basis points
Residential Mortgage Sub Servicing Loan [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	42,100,000,000	46,600,000,000	42,100,000,000	46,600,000,000	12,500,000,000
Commercial Mortgage Loans [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	11,300,000,000	11,400,000,000	11,300,000,000	11,400,000,000	10,600,000,000
Commercial Mortgage Loans [Member]
Servicing Assets at Fair Value [Line Items]
Mortgage loans serviced for others	3,500,000,000	4,400,000,000	3,500,000,000	4,400,000,000	3,800,000,000
Estimated fair value of capitalized mortgage loan servicing assets	$ 87,000,000	$ 85,000,000	$ 87,000,000	$ 85,000,000
Weighted average discount rates used to estimate fair value of capitalized mortgaged loan servicing assets	18.00%	18.00%