Summary of Significant Accounting Policies (Details 5) (USD $) In Billions, unless otherwise specified	1 Months Ended	12 Months Ended
	Dec. 31, 2009	Dec. 31, 2012 item
Intangible Assets
Number of interest rate swaps		1
Recent accounting and Regulatory Pronouncements
Percentage of insured deposits required to be maintained under the FDIC's Deposit Insurance Fund		1.35%
Minimum assets with banks required for closing any shortfall by FDIC's Deposit Insurance Fund		$ 10.0
Minimum asset requirement of institutions that are prohibited from including trust preferred securities (TRUPs) as Tier 1 capital beginning in 2013	$ 15
Portion of Tier 1 capital to be phased out in next two years		0.33
Period over which one-third portion of Tier 1 Capital will be phased out		2 years
Savannah
Intangible Assets
Number of interest rate swaps contracts that were classified as non-designated hedges acquired through merger		2
Minimum
Intangible Assets
Estimated useful lives of core deposit intangibles		2 years
Maximum
Intangible Assets
Estimated useful lives of core deposit intangibles		15 years
Core deposit intangibles | Minimum
Intangible Assets
Estimated useful lives of core deposit intangibles		7 years
Core deposit intangibles | Maximum
Intangible Assets
Estimated useful lives of core deposit intangibles		13 years
Noncompete intangibles | Minimum
Intangible Assets
Estimated useful lives of core deposit intangibles		2 years
Noncompete intangibles | Maximum
Intangible Assets
Estimated useful lives of core deposit intangibles		3 years
Client list intangibles
Intangible Assets
Estimated useful lives of core deposit intangibles		15 years