Derivatives - Summary of gains (losses) for derivative instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivatives
Net derivative gain related to mortgage servicing rights		$ 10	$ 29
Interest rate lock commitments expected to close | Gain on mortgage loans, net
Derivatives
Gains (losses) on derivative instruments	$ 200	315	261
Forward delivery commitments | Gain on mortgage loans, net
Derivatives
Gains (losses) on derivative instruments	(8)	(1)	(7)
Option contracts | Gain on mortgage loans, net
Derivatives
Gains (losses) on derivative instruments	(1)	0	(2)
MSR-related agreements | Net derivative gain (loss) related to mortgage servicing rights
Derivatives
Net derivative gain related to mortgage servicing rights	$ 0	$ 10	$ 29