Equity Compensation Plans (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Percentage of stock options vesting in a period of one year	50.00%
Percentage of stock options vesting in the remaining following years	50.00%
Duration of period in which grants of restricted stock are released after grant date	4 years
Number of shares available for grant	19
Weighted average fair value per option granted	$ 13.23	$ 15.63	$ 15.00
Stock option expense reduced operating earnings	$ 88	$ 90	$ 82
Stock option expense earnings per share	$ 0.16	$ 0.16	$ 0.14
Unrecognized compensation cost related to stock	56
Total intrinsic value of options exercised	112	113	109
Cash received from the exercise of stock options	146	198	277
Excess tax benefit from exercise of stock options	29	24	18
Stock Options
Awards of stock options vest over number of years	2 years
Period of restriction lapses in which compensation cost is expected to be recognized over a weighted average period (in years)	1 year
Restricted Stock Units
Stock option expense reduced operating earnings	26	38	36
Stock option expense earnings per share	$ 0.05	$ 0.07	$ 0.06
Total fair value of shares vested	28	28	30
Restricted Stock and Restricted Stock Units (RSUs)
Unrecognized compensation cost related to stock	$ 52
Period of restriction lapses in which compensation cost is expected to be recognized over a weighted average period (in years)	2 years 3 months 18 days
Maximum | Stock Options
Stock options expiration period	7 years
Minimum | Stock Options
Stock options expiration period	5 years