Fair Value Disclosures - Measured on a Nonrecurring Basis (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Carrying Value
Impaired loans			$ 314	$ 131
Foreclosed real estate			58	85
Valuation Adjustments
Impaired loans	$ (22)	$ (6)	(76)	(19)
Foreclosed real estate	$ (59)	$ (54)	$ (160)	$ (137)