Credit Risk (Details 2) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Loss Contingency [Abstract]
Estimated amount of reasonably possible losses in excess of the recorded liability	$ 150
Changes in repurchase and foreclosure-related reserves
Balance, beginning of period	89	$ 93
Realized losses	(12)	(13)
Increase in reserves due to:
Changes in assumptions	3	6
New loan sales	4	6
Balance, end of period	84	$ 92
Loan repurchase and indemnification liability	62		$ 62
Loans with full risk of loss or with respect to which the company has identified a breach of representation and warranty provisions	$ 171
Percentage of loans with full risk of loss or with respect to which the company has identified a breach of representation and warranty provisions and are at least 90 days delinquent	11.00%
Recourse obligations
Loss Contingency [Abstract]
Estimated amount of reasonably possible losses in excess of the recorded liability	$ 40