Stockholders' Equity (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended				1 Months Ended	12 Months Ended		0 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Regulatory Requirements [Member]	Apr. 30, 2011 $ 250 Million Dollar Authorization [Member]	Dec. 31, 2011 $ 250 Million Dollar Authorization [Member]	Dec. 31, 2010 $ 250 Million Dollar Authorization [Member]	Feb. 06, 2012 $1 Billion Authorization [Member]	Apr. 30, 2011 $1 Billion Authorization [Member]	Dec. 31, 2011 $1 Billion Authorization [Member]
Equity, Class of Treasury Stock [Line Items]
Expiration date of new authorization	June 30, 2013
Share repurchase authorization					$ 250,000,000				$ 1,000,000,000
Shares repurchased in open market						0.80	1.99			5.90
Value of shares repurchased						53,000,000	100,000,000			439,000,000
Shares repurchased in open market, average price						$ 63.73	$ 50.17			$ 74.01
Remaining authorized amount under new authorization								561,000,000
Common shares acquired in connection with employee stock plans, shares	0.8	0.2	0.6
Common shares acquired in connection with employee stock plans, amount	49,000,000	8,000,000	23,000,000
Aggregate statutory capital and surplus in our state regulated subsidiaries	4,700,000,000	4,300,000,000
Dividends which may be paid to the parent company without prior approval by state regulatory authorities	$ 970,000,000			$ 740,000,000