Capital Stock (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock repurchase program, authorized amount	$ 3,400,000,000
Available to repurchase common stock	335,600,000
Amount expended on share repurchases in open market transactions	251,008,000	424,849,000	433,739,000
Restricted shares turned in for tax withholding (in shares)	269,745	182,203	123,489
Total value of withheld stock	20,170,000	13,262,000	6,298,000
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Open Market Purchases [Member]
Amount expended on share repurchases in open market transactions	251,000,000	424,800,000	434,800,000
Number of shares repurchased	3,550,817	6,275,470	8,157,400
Average per share price on share repurchases in open market transactions	$ 70.69	$ 67.70	$ 53.31
Cash and premiums received under stock repurchase agreement			16,100,000
Structured Repurchase Agreements [Member]
Up-front payment for structured treasury stock repurchase agreement			$ 15,000,000