MSR (Activity Related to Mortgage Banking Net Revenue) (Parenthetical) (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	[2]	Dec. 31, 2015
Mortgage Loans on Real Estate
Residential mortgage loan sales	[1]		$ 6,369	$ 6,927		$ 5,078
Residential Mortgage Loans | Troubled Debt Restructuring On Nonaccrual Status
Mortgage Loans on Real Estate
Residential mortgage loan sales		$ 568

[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 d uring the first quarter of 2015.