Fair Value (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Measurements, Nonrecurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 187		$ 250
Nonrecurring Assets - Gains (Losses)	(25)	$ (7)
Nonaccrual Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	137		100
Nonrecurring Assets - Gains (Losses)	(23)	(6)
OREO, Foreclosed and Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	35		70
Nonrecurring Assets - Gains (Losses)		(4)
Long-lived Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	15		$ 80
Nonrecurring Assets - Gains (Losses)	$ (2)	$ 3