Fair Value (Fair Value Measurements- Nonrecurring Quantitative Information) (Details) - Fair Value, Measurements, Nonrecurring [Member] - Level 3 [Member] - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 294,000,000	$ 195,000,000
Nonaccrual Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	184,000,000	30,000,000
Nonaccrual Loans [Member] | LGD percentage [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 82,000,000	$ 20,000,000
Nonaccrual Loans [Member] | LGD percentage [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loss Severity	3.20%	8.10%
Nonaccrual Loans [Member] | LGD percentage [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loss Severity	70.10%	73.30%
Nonaccrual Loans [Member] | LGD percentage [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loss Severity	32.20%	58.60%
Nonaccrual Loans [Member] | Fair Value Of Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 102,000,000	$ 10,000,000
OREO and Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	103,000,000	137,000,000
OREO and Foreclosed Assets [Member] | Fair Value Of Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	103,000,000	137,000,000
Insignificant Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Nonrecurring Assets - Fair Value	$ 7,000,000	$ 28,000,000