Capital Stock (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended				15 Months Ended	31 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jan. 31, 2018	Jul. 31, 2017	Oct. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Class of Stock [Line Items]
Common stock, shares authorized (in shares)		12,000,000,000
Increase in quarterly dividend rate	8.20%
Cash dividends declared (USD per share)	$ 0.66	$ 2.54	$ 0.61	$ 2.35	$ 2.17
Annualized dividend rate (USD per share)		$ 2.64
Repurchase of common stock (in shares)		41,604,141		16,221,001	10,682,419
Average price of repurchased shares (USD per share)		$ 70.10		$ 63.48	$ 51.83
Aggregate cost of shares repurchased		$ 2,917,000,000		$ 1,030,000,000	$ 554,000,000
July 2014 Share Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount											$ 1,000,000,000
Repurchase of common stock (in shares)						20,400,000
Average price of repurchased shares (USD per share)						$ 48.90
July 2015 Share Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount								$ 4,000,000,000	$ 3,000,000,000	$ 1,000,000,000
Repurchase of common stock (in shares)		41,600,000		16,200,000	600,000
Average price of repurchased shares (USD per share)		$ 70.10			$ 57.66
Aggregate cost of shares repurchased				$ 1,030,000,000	$ 35,000,000
Amount remaining in the share repurchased program		$ 18,000,000
Serial Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		10,000,000
Preferred stock, par value (USD per share)		$ 1.00
Preferred stock, shares issued (in shares)		0
Stock Compensation Plan [Member]
Class of Stock [Line Items]
Shares of common stock reserved for stock-based awards (in shares)		41,688,666
Subsequent Event [Member] | July 2015 Share Repurchase Program [Member]
Class of Stock [Line Items]
Repurchase of common stock (in shares)							58,700,000
Average price of repurchased shares (USD per share)							$ 68.15
Subsequent Event [Member] | January 2018 Share Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount							$ 1,000,000,000.0