Capital Stock (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended			15 Months Ended	18 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2013	Jul. 31, 2015	Jul. 31, 2014	Aug. 31, 2013	Apr. 30, 2013	Oct. 31, 2012	Oct. 31, 2011
Class of Stock [Line Items]
Common stock, shares authorized (in shares)			12,000,000,000
Cash dividends declared (USD per share)	$ 0.565	$ 0.52	$ 2.17	$ 2.00	$ 1.84
Annualized dividend rate (USD per share)	$ 2.26
Repurchase of common stock (in shares)			10,682,419	22,452,599	16,652,913
Aggregate cost of shares repurchased			$ 554,000,000	$ 939,000,000	$ 600,000,000
Average price of repurchased shares (USD per share)			$ 51.83	$ 41.79	$ 36.05
October 2011 Share Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount													$ 1,500,000,000	$ 1,000,000,000
Repurchase of common stock (in shares)								48,300,000
Average price of repurchased shares (USD per share)								$ 31.06
April 2013 Share Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount											$ 1,000,000,000	$ 300,000,000
Repurchase of common stock (in shares)							27,100,000
Average price of repurchased shares (USD per share)							$ 36.97
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									$ 1,000,000,000.0
Repurchase of common stock (in shares)			600,000
Aggregate cost of shares repurchased			$ 35,000,000
Average price of repurchased shares (USD per share)			$ 57.66
Amount remaining in the share repurchased program			$ 965,000,000
Serial Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			10,000,000
Preferred stock, par value			$ 1.00
Preferred stock, shares issued (in shares)			0
Common Stock [Member] | Dividend Declared [Member]
Class of Stock [Line Items]
Increase in quarterly dividend rate	8.70%
Stock Compensation Plan [Member]
Class of Stock [Line Items]
Shares of common stock reserved for stock-based awards (in shares)			42,209,751