Goodwill and Other Intangible Assets (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended							12 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2011 Austin Capital Management [Member]	Dec. 31, 2010 Austin Capital Management [Member]	Dec. 31, 2011 Community Banking [Member]	Dec. 31, 2010 Community Banking [Member]	Dec. 31, 2009 Community Banking [Member]	Mar. 31, 2009 Corporate Banking [Member]	Dec. 31, 2011 Corporate Banking [Member]	Dec. 31, 2010 Corporate Banking [Member]	Dec. 31, 2009 Corporate Banking [Member]	Dec. 31, 2011 Core deposit intangibles [Member]	Dec. 31, 2010 Core deposit intangibles [Member]	Dec. 31, 2011 Other intangible assets [Member]	Dec. 31, 2010 Other intangible assets [Member]
Gross carrying amount and the accumulated amortization of intangible assets
Gross Carrying Amount	$ 207	$ 207													$ 65	$ 65	$ 142	$ 142
Accumulated Amortization	190	186													48	44	142	142
Goodwill and Other Intangible Assets (Textual) [Abstract]
Pre tax impairment charge based on additional impairment testing											223
Accumulated Impairment loss								0	0	0		665	665	665
Gross carrying amount						18	18
Accumulated Amortization						18	18
Additional Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated fair value of the Community Banking unit greater than certain percent of carrying value				11.00%	18.00%
Expected deductible goodwill for tax purpose	122
Write off of intangible asset related to customer relationships		15
Intangible asset related to vendor relationships			45
Write off of intangible asset related to vendor relationships			45
Intangible asset amortization expense	4	13	76
Estimated amortization expense for intangible assets in 2012	4
Estimated amortization expense for intangible assets in 2013	4
Estimated amortization expense for intangible assets in 2014	3
Estimated amortization expense for intangible assets in 2015	2
Estimated amortization expense for intangible assets in 2016	$ 2