Sales of Receivables and Servicing Rights - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Mortgage Loans On Real Estate [Line Items]
Residential mortgage loan sales	$ 1,001,000,000	[1],[2]	$ 1,672,000,000	[1]
Sevicing of residential mortgage loans for other investors	64,200,000,000				65,400,000,000
Residential Mortgage Loans | Troubled Debt Restructuring
Mortgage Loans On Real Estate [Line Items]
Gain on sale of HFS loans	$ 37,000,000

[1] Represents the unpaid principal balance at the time of the sale.

[2] Excludes $568 of HFS residential mortgage loans previously modified in a TDR that were sold during the first quarter of 2015.