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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 153		$ 153		$ 250
Nonrecurring Assets - Gains (Losses)	(14)	$ (9)	(17)	$ (32)
Nonaccrual Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	97		97		100
Nonrecurring Assets - Gains (Losses)	(11)	(1)	(14)	(11)
OREO and Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	53		53		70
Nonrecurring Assets - Gains (Losses)	(2)	(5)	(2)	(10)
Long-lived Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	3		3		$ 80
Nonrecurring Assets - Gains (Losses)	$ (1)	$ (3)	$ (1)	$ (11)