Shareholders' Equity (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended				6 Months Ended	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2012 Stock incentive plan [Member]	Mar. 31, 2012 Annual Co-CEO Equity Bonus Plan [Member]	Jun. 30, 2012 Voting Preferred Stock [Member]	Jun. 30, 2012 Nonvoting Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, shares authorized									12,500,000	12,500,000
Preferred Stock, par value									$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Other benefit plans, shares								111,270
Common Stock issued, fair value per share								$ 38.38
Common Stock options issued under stock incentive plan							1,100,000
Common Stock options issued under stock incentive plan, average exercise price							$ 38.11
Stockholders' Equity (Textual) [Abstract]
Expected dividend yield			1.80%
Expected volatility			39.00%
Expected term (in years)			7 years 3 months 18 days
Risk-free rate			1.40%
Restricted Common Stock, shares issued			131,731
Restricted Common Stock, fair value per share			$ 38.11
Fair value per share of options granted			$ 13.02
Total compensation expense related to stock incentive plans	$ 9	$ 5	$ 15	$ 10
Net of tax unrealized gains (losses) related to credit-only impaired securities	$ (1)		$ (1)		$ (8)	$ (16)