Fair Value (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Measurements, Nonrecurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 248		$ 248		$ 313
Nonrecurring Assets - Gains (Losses)	(9)	$ (38)	(32)	$ (101)
Nonaccrual Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	130		130		187
Nonrecurring Assets - Gains (Losses)	(1)	(32)	(11)	(81)
OREO, Foreclosed and Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	82		82		107
Nonrecurring Assets - Gains (Losses)	(5)	(6)	(10)	(15)
Insignificant Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	36		36		$ 19
Nonrecurring Assets - Gains (Losses)	$ (3)		$ (11)	$ (5)