Acquisition and Discontinued Operations (Details 6) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Components of Income (Loss) from Discontinued Operations, Net of Taxes, of Subsidiary
Noninterest income	$ 485	$ 454	$ 957	$ 911
Noninterest expense	714	680	1,417	1,381
Income taxes	57	94	132	205
Income (loss) from discontinued operations, net of taxes	10	(9)	5	(20)
Community Bank [Member]
Components of Income (Loss) from Discontinued Operations, Net of Taxes, of Subsidiary
Noninterest income	189	185	365	371
Income taxes	9	(1)	21	25
Income (loss) from discontinued operations, net of taxes
Segment, Discontinued Operations [Member]
Components of Income (Loss) from Discontinued Operations, Net of Taxes, of Subsidiary
Noninterest income	2	11	20	20
Noninterest expense	10	9	27	21
Income (loss) before income taxes	16	(15)	8	(32)
Income taxes	6	(6)	3	(12)
Income (loss) from discontinued operations, net of taxes	10	(9)	5	(20)
Segment, Discontinued Operations [Member] | Austin Capital Management [Member]
Components of Income (Loss) from Discontinued Operations, Net of Taxes, of Subsidiary
Noninterest income				1
Noninterest expense	1		9	1
Income (loss) before income taxes	(1)		(9)
Income taxes			(3)
Income (loss) from discontinued operations, net of taxes	$ (1)		$ (6)