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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2013 Stock Incentive Plan [Member]	Mar. 31, 2013 Annual Equity Bonus 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
Other benefit plans, shares								88,602
Common Stock issued, fair value per share								$ 47.12
Compensation expense related to stock incentive plans	$ 7	$ 9	$ 20	$ 15
Stockholders' Equity (Textual) [Abstract]
Net of tax unrealized gains (losses) related to credit-only impaired securities	$ 42		$ 42		$ 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%