Loan Servicing - Analysis of Activity in Residential MSRs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Servicing Asset at Fair Value, Amount [Roll Forward]
MSRs, carrying value, beginning of period	$ 1,056
Change in fair value due to changes in valuation inputs or assumptions:
MSRs, carrying value, end of period	1,119
Residential MSRs
Servicing Asset at Fair Value, Amount [Roll Forward]
MSRs, carrying value, beginning of period	914	$ 915
Additions	28	38
Change in fair value due to changes in valuation inputs or assumptions:
Prepayment speeds	61	17
OAS	2	0
Servicing Costs	0	9
Realization of expected net servicing cash flows, passage of time and other	(32)	(33)
MSRs, carrying value, end of period	973	946
Gains (losses) on derivative financial instruments used to mitigate the income statement effect of changes in residential MSR fair value	$ (63)	$ (20)