Share-Based Compensation Plans (Details 5) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 United States	Dec. 31, 2011 United States	Dec. 31, 2010 United States	Dec. 31, 2012 United States Maximum	Dec. 31, 2012 United Kingdom	Dec. 31, 2011 United Kingdom	Dec. 31, 2010 United Kingdom	Dec. 31, 2008 United Kingdom Maximum	Dec. 31, 2006 United Kingdom Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Purchase of shares under plan							7,500,000				200,000	525,000
Period of interval for purchase of common stock					6 months	3 months
Purchase price expressed as a percentage of the fair market value of common stock					85.00%	85.00%
Stock issued to employees under the plan (in shares)				621,000	468,000	357,000		25,000	63,000	5,000
Compensation expense	$ 212	$ 235	$ 221	$ 6	$ 5	$ 3		$ 1	$ 1	$ 1
Waiting period before purchase of shares								3 years