MSR (Fair Value of the Servicing Rights) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Servicing Assets at Fair Value
Fair value at beginning of period	$ 744
Fair value at end of period	858	$ 744
Fixed Rate Residential Mortgage Loans
Servicing Assets at Fair Value
Fair value at beginning of period	722	757
Fair value at end of period	841	722
Adjustable Rate Residential Mortgage Loans
Servicing Assets at Fair Value
Fair value at beginning of period	22	27
Fair value at end of period	17	22
Fixed Rate Automobile Loans
Servicing Assets at Fair Value
Fair value at beginning of period	0	1
Fair value at end of period	$ 0	$ 0