Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Core Deposits Member	Dec. 31, 2012 Other Intangible Assets [Member]	Dec. 31, 2012 Land Improvements [Member] MaximumMember	Dec. 31, 2012 Land Improvements [Member] MinimumMember	Dec. 31, 2012 Building and Building Improvements [Member] MaximumMember	Dec. 31, 2012 Building and Building Improvements [Member] MinimumMember	Dec. 31, 2012 Computer Equipment [Member] MaximumMember	Dec. 31, 2012 Computer Equipment [Member] MinimumMember	Dec. 31, 2012 Furniture and Fixtures [Member] MaximumMember	Dec. 31, 2012 Furniture and Fixtures [Member] MinimumMember
Accounting Policies [Abstract]
Other real estate owned	$ 35	$ 41
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant, and equipment					15 years	3 years	39 years	5 years	5 years	3 years	15 years	3 years
Finite-Lived Intangible Assets [Line Items]
Weighted average lives of finite-lived intangilbe assets			10 years	14 years