Loan Servicing - Analysis of Activity in Residential MSRs (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Servicing Asset at Fair Value, Amount [Roll Forward]
MSRs, carrying value, beginning balance	$ 1,056
Change in fair value due to changes in valuation inputs or assumptions:
MSRs, carrying value, ending balance	1,143
Residential MSRs
Servicing Asset at Fair Value, Amount [Roll Forward]
MSRs, carrying value, beginning balance	914	$ 915
Additions	63	63
Change in fair value due to changes in valuation inputs or assumptions:
Prepayment speeds	67	(45)
OAS	17	42
Servicing costs	0	9
Realization of expected net servicing cash flows, passage of time and other	(70)	(69)
MSRs, carrying value, ending balance	991	915
Gains (losses) on derivative financial instruments used to mitigate the income statement effect of changes in residential MSR fair value	$ (84)	$ 3