Net Income Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
NUMERATOR:
Net income	$ 224	$ 228	$ 283	$ 327
Incremental income effect of interest on 5.25% convertible notes	1	1	1	1
Net income after assumed conversion	$ 225	$ 229	$ 284	$ 328
DENOMINATOR:
Weighted-average shares outstanding, basic	714	757	719	764
Dilutive effect of Employee stock options and restricted stock units	2	1	2	1
Dilutive effect of 5.25% convertible notes	6	6	6	6
Adjusted weighted-average shares outstanding, diluted	722	764	727	771
NET INCOME PER SHARE:
Basic	$ 0.31	$ 0.30	$ 0.39	$ 0.43
Diluted	$ 0.31	$ 0.30	$ 0.39	$ 0.43
Stock options and restricted stock units
Potentially dilutive amounts excluded from calculations:
Stock options and restricted stock units	10	42	15	43