Loan Servicing - Summary of Commercial Mortgage Banking Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Transfers and Servicing [Abstract]
UPB of CRE mortgages serviced for others	$ 28,441	$ 29,333
CRE mortgages serviced for others covered by recourse provisions	4,153	4,240
Maximum recourse exposure from CRE mortgages sold with recourse liability	1,218	1,272
Recorded reserves related to recourse exposure	5	7
Originated CRE mortgages during the year	6,753	7,145
Servicing Assets at Fair Value [Line Items]
MSRs at fair value	1,056	1,052
CRE
Servicing Assets at Fair Value [Line Items]
MSRs at fair value	$ 142	$ 137