Fair Value (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Other noninterest-bearing investments valued under the cost method	$ 13,300,000	$ 25,300,000
Fair value of AFS securities	13,372,194,000	7,643,116,000
Principal amount of other real estate owned property sold	12,800,000	19,200,000
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	211,400,000	191,500,000
OREO Properties [Member]
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	3,700,000	4,000,000
Impairment of OREO properties	200,000	600,000
Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	13,188,495,000	7,581,309,000
Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	0	$ 0
Third Party Pricing Service [Member] | Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	$ 0.91