Capital Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017
Capital Stock [Line Items]
Common and Preferred Stock, shares authorized (in shares)	1,000,500,000
Preferred Stock, Shares Authorized	500,000
Preferred stock, par per share	$ 1
Common stock, authorized (in shares)	1,000,000,000	1,000,000,000		1,000,000,000
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Shares repurchased (in shares)	1,900,000	100,000	7,400,000
Repurchase and retirement of shares of common stock	$ 230
Remaining shares authorized to be repurchased	$ 1,640
Capital shares reserved for future issuance	37,000,000	11,000,000
Aggregate intrinsic value of options exercised	$ 184	$ 128	$ 98
Options exercised during period, exercise price range, lower range limit	$ 38.71
Options exercised during period, exercise price range, upper range limit	$ 154.87
Compensation cost not yet recognized	$ 90
Compensation cost not yet recognized, period for recognized	1 year 7 months
Restricted Stock Units (RSUs)
Capital Stock [Line Items]
Compensation cost not yet recognized	$ 56
Compensation cost not yet recognized, period for recognized	1 year
Weighted average grant date fair value, Granted (in dollars per share)	$ 117.44	$ 94.70
Shares vested during the period	$ 44
Performance Stock Units (PSUs)
Capital Stock [Line Items]
Compensation cost not yet recognized	$ 13
Compensation cost not yet recognized, period for recognized	1 year
Weighted average grant date fair value, Granted (in dollars per share)	$ 122.41
Shares vested during the period	$ 0
Employee Stock Purchase Plans
Capital Stock [Line Items]
Percentage of closing stock price under ESPP	95.00%
Shares issued under the ESPP	163,415	159,329