Equity Compensation Plans (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Awards of stock options vest over number of years	two
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%
Exercise price of common stock available not less than fair market value, percentage	80.00%
Number of shares available for grant	19
Duration of period in which grants of restricted stock are released after grant date	four
Vesting period of compensation expense related to stock	two
Weighted average fair value per option granted	$ 15.63	$ 15.00	$ 6.98
Stock option expense reduced operating earnings	$ 90	$ 82	$ 83
Stock option expense earnings per share	$ 0.16	$ 0.14	$ 0.14
Unrecognized compensation cost related to stock	73
Period of restriction lapses in which compensation cost is expected to be recognized over a weighted average period (in years)	1
Total intrinsic value of options exercised	113	109	32
Cash received from the exercise of stock options	198	277	142
Excess tax benefit resulting from stock option exercises	24	18	5
Compensation expense related to restricted stock and restricted stock units, recognition period (in years)	four
Restricted Stock Units [Member] | Restricted Stock [Member]
Stock option expense reduced operating earnings	38	36	34
Stock option expense earnings per share	$ 0.07	$ 0.06	$ 0.06
Unrecognized compensation cost related to stock	56
Period of restriction lapses in which compensation cost is expected to be recognized over a weighted average period (in years)	2.4
Total fair value of shares vested	$ 28	$ 30	$ 29
Three Years Exercisable [Member]
Options exercisable after date of grant depending on terms of specific award, years	three
Five Years Exercisable [Member]
Options exercisable after date of grant depending on terms of specific award, years	five
Maximum [Member]
Expiration of stock options awarded after grant date, in years	seven
Minimum [Member]
Expiration of stock options awarded after grant date, in years	five