Fair Value (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 250	$ 312
Nonrecurring Assets - Gains (Losses)	(186)	(137)	$ (82)
Nonaccrual Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	100	187
Nonrecurring Assets - Gains (Losses)	(8)	(106)	(44)
OREO, Foreclosed and Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	70	107
Nonrecurring Assets - Gains (Losses)	(10)	(16)	(18)
Long-lived Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	80	18
Nonrecurring Assets - Gains (Losses)	$ (168)	$ (15)	$ (20)