Shareholders' Equity Shareholders' Equity (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended						3 Months Ended								12 Months Ended								3 Months Ended	12 Months Ended							3 Months Ended	12 Months Ended	5 Months Ended		1 Months Ended			3 Months Ended				12 Months Ended
	Dec. 31, 2012		Nov. 30, 2012		Oct. 31, 2012		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010	Jan. 22, 2013	Jun. 30, 2010	Dec. 31, 2012 Stock Option	Dec. 31, 2012 Restricted Stock	Mar. 31, 2010 Common Stock	Dec. 31, 2012 Common Stock	Dec. 31, 2011 Common Stock	Dec. 31, 2010 Common Stock	Apr. 24, 2012 Common Stock	Nov. 30, 2010 Common Stock	Dec. 31, 2012 Warrants	Nov. 30, 2010 Warrants	Mar. 31, 2010 Nonredeemable Preferred Stock	Dec. 31, 2010 Nonredeemable Preferred Stock	Dec. 31, 2011 Sterling Bancshares	Jul. 31, 2011 Sterling Bancshares	Dec. 31, 2012 Share Repurchase Program	Nov. 30, 2012 Share Repurchase Program	Oct. 31, 2012 Share Repurchase Program	Dec. 31, 2012 Share Repurchase Program	Sep. 30, 2012 Share Repurchase Program	Jun. 30, 2012 Share Repurchase Program	Mar. 31, 2012 Share Repurchase Program	Dec. 31, 2012 Share Repurchase Program	Dec. 31, 2011 Share Repurchase Program
Stock Repurchase Program, Authorized Amount															$ 375
Purchase of common stock															(308)		(116)	(4)																								(304)
Total Number of Shares Purchased	500,000	[1]	1,274,000	[1]	1,346,000	[1]	3,120,000	[1]	2,931,000	[1]	2,908,000	[1]	1,257,000	[1]	10,216,000	[1]								10,200,000	4,300,000	100,000									500,000	1,274,000	1,343,000	3,117,000	2,928,000	2,884,000	1,125,000	10,054,000	4,100,000
Percentage Increase in Dividend Per Share Capital Plan	50.00%						50.00%								50.00%				13.00%
Increase Dividend Per Share Capital Plan																			$ 0.17
Cash dividends declared per common share											$ 0.15		$ 0.10		$ 0.55		$ 0.40	$ 0.25
Number of shares authorized to be repurchased																											5,700,000	12,600,000		11,500,000
Shares issued in connection with acquisition of Sterling Bancshares, Inc.																									24,300,000								24,300,000
Value of shares issued in connection with acquisition of Sterling Bancshares, Inc.																	803								122								793
Exercise price to purchase securities granted by warrants																				29.40														30.36
Value of stock options acquired in connection with acquistion of Sterling Bancshares, Inc.																																		3
Fair value of warrants	124						124								124																			7
Redemption of preferred stock																		2,250													2,250	2,250
Issuance of common stock																		849					880			125
Redemption discount accretion on preferred stock																		0													94	(94)
Preferred stock dividends																																24
Redemption discount accretion on preferred stock effect on diluted earnings per share																																$ 0.54
Accretion of discount on preferred stock																		$ 0														$ 5
Cumulative impact of preferred stock redemption including redemption charge, cash dividends, and non-cash discount accretion on diluted earnings per share																																$ 0.71
Number of securities to purchase granted by warrant																				11,500,000
Common stock shares reserved for future issuance																					18,400,000								12,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number																						2,400,000

[1] Includes approximately 162,000 shares shares purchased pursuant to deferred compensation plans and shares purchased from employees to pay for taxes related to restricted stock vesting under the terms of an employee share-based compensation plan during the year ended December 31, 2012 . These transactions are not considered part of the Corporation's repurchase program.