Fair Value (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 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	330,000,000		330,000,000		211,000,000
Net gains on sale of OREO properties	0	$ 1,000,000	0	$ 2,000,000
Principal amount of other real estate owned property sold			3,000,000	5,000,000
Equity Method Investments, Fair Value Disclosure	38,000,000		38,000,000		35,000,000
OREO Properties [Member]
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	0	$ 1,000,000	0	$ 3,000,000
Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	15,262,000,000		15,262,000,000		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