Shareholders' Equity (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense related to stock incentive plans	$ 13	$ 6
Stockholders' Equity (Textual) [Abstract]
Net of tax unrealized gains (losses) related to credit-only impaired securities	$ 45		$ 33
Fair value per share of options granted	$ 15.10
Expected dividend yield	1.80%
Expected volatility	38.80%
Expected term (in years)	7 years 3 months 18 days
Risk-free rate	1.40%
Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Common Stock, shares issued	249,411
Restricted Common Stock, fair value per share	$ 44.01
Common Stock options issued under stock incentive plan	1,000,000
Common Stock options issued under stock incentive plan, average exercise price	$ 44.01
Annual Equity Bonus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Other benefit plans, shares	88,602
Common Stock issued, fair value per share	$ 47.12