Mortgage Banking Activities, Analysis of Changes in Liability for Mortgage Loan Repurchase Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Liability For Mortgage Loan Repurchase Losses [Abstract]
Balance, beginning of period	$ 255	$ 557	$ 378	$ 615
Provision for repurchase losses:
Loan sales	11	11	26	34
Change in estimate	(24)	(17)	(132)	(74)
Net reductions	(13)	(6)	(106)	(40)
Losses	(3)	(13)	(33)	(37)
Balance, end of period	239	$ 538	239	$ 538
Liability For Mortgage Loans Repurchase Losses [Member]
Mortgage Banking Activities (Textual) [Abstract]
Range of possible loss, portion not accrued	$ 191		$ 191