Fair Value (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Other noninterest-bearing investments valued under the cost method	$ 10,000,000		$ 10,000,000		$ 13,000,000
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	324,000,000		324,000,000		211,000,000
Net gains on sale of OREO properties	(1,000,000)	$ 0	(1,000,000)	$ (2,000,000)
Principal amount of other real estate owned property sold			5,000,000	8,000,000
Equity Method Investments, Fair Value Disclosure	35,000,000		35,000,000		38,000,000
OREO Properties [Member]
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	1,000,000		2,000,000	$ 3,000,000
Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	15,131,000,000		15,131,000,000		13,188,000,000
Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	0		0		0
Third Party Pricing Service [Member] | Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	$ 0.92		$ 0.92		$ 0.91