Shareholders' Equity and Dividend Availability (details) - Share Repurchases (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2012 Board of Directors Approved Repurchase Authorizations [Member]	Sep. 30, 2012 Board of Directors Approved Repurchase Authorizations [Member]	Jun. 30, 2012 Board of Directors Approved Repurchase Authorizations [Member]	Mar. 31, 2012 Board of Directors Approved Repurchase Authorizations [Member]	Dec. 31, 2012 Board of Directors Approved Repurchase Authorizations [Member]	Dec. 31, 2012 Amended and Restated 2004 Stock Incentive Plan Repurchases [Member]	Dec. 31, 2011 Amended and Restated 2004 Stock Incentive Plan Repurchases [Member]
Repurchase activity
Number of shares purchased (in shares)	5.4	5.4	5.6	6.0	22.4
Cost of shares repurchased	$ 400	$ 350	$ 350	$ 350	$ 1,450
Average price paid per share	$ 73.00	$ 65.00	$ 62.40	$ 58.73	$ 64.64
Remaining capacity under share repurchase authorization	2,159	2,559	2,909	3,259	2,159
Shares acquired to cover tax withholding costs and exercise costs						$ 55	$ 82