Sales of Receivables and Servicing Rights - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2015	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Servicing Rights at Fair Value
Residential mortgage loan sales	[2]		$ 5,078	[1]	$ 5,467	$ 21,529
Sevicing of residential mortgage loans for other investors			59,000		65,400
Amortization			$ (140)		$ (121)	$ (168)
Residential Mortgage Loans | Troubled Debt Restructuring
Servicing Rights at Fair Value
Gain on sale of HFS loans		$ 37
Residential mortgage loan sales		$ 568

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

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