Capital Stock and Stock-Based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 19, 2015
Preference Stock [Abstract]
Shares authorized (in shares)	50,262,150
Stock Repurchases [Abstract]
Repurchased stock	$ 1,551	$ 1,530	$ 1,521
Summary of common stock activity [Roll Forward]
Common Stock Balance, January 1 (in shares)	906,712,145	919,946,575	935,728,676
Common stock acquired (in shares)	(22,802,784)	(23,131,081)	(25,573,317)
Shares issued for stock options (in shares)	7,394,839	7,977,124	7,883,834
Shares issued for restricted stock and other (in shares)	1,434,318	1,919,527	1,907,382
Common Stock Balance, December 31 (in shares)	892,738,518	906,712,145	919,946,575
Summary Of Treasury Stock Activity [Roll Forward]
Treasury Stock Balance, January 1 (in shares)	558,994,215	545,759,785	529,977,684
Common stock acquired (in shares)	22,802,784	23,131,081	25,573,317
Shares issued for stock options (in shares)	(7,394,839)	(7,977,124)	(7,883,834)
Shares issued for restricted stock and other (in shares)	(1,434,318)	(1,919,527)	(1,907,382)
Treasury Stock Balance, December 31 (in shares)	572,967,842	558,994,215	545,759,785
Stock-based compensation [Abstract]
Allocated Share-based Compensation Expense	$ 125	$ 131	$ 128
Total income tax benefit	$ 39	$ 42	$ 39
Fair Value Assumptions [Abstract]
Weighted-average estimated fair value of stock options granted (in dollars per share)	$ 7.25	$ 7.60	$ 7.41
Expected term (in years)	4 years 6 months	4 years 6 months	4 years 6 months
Expected Volatility Rate (in hundredths)	17.60%	17.10%	18.40%
Risk-Free Rate (in hundredths)	1.50%	1.60%	1.50%
Expected Dividend Yield (in hundredths)	2.50%	2.30%	2.30%
Summary of restricted stock award activity [Roll Forward]
Restricted stock awards - beginning balance (in shares)	3,694,000
Granted (in shares)	950,000
Vested (in shares)	(1,364,000)
Forfeited (in shares)	(114,000)
Restricted stock awards - ending balance (in shares)	3,166,000	3,694,000
Weighted average grant date fair value per award [Roll Forward]
Weighted average grant date fair value of restricted stock awards - beginning of period (in dollars per share)	$ 56
Weighted average grant date fair value of restricted stock awards - shares granted (in dollars per share)	66
Weighted average grant date fair value of restricted stock awards - shares vested (in dollars per share)	51
Weighted average grant date fair value of restricted stock awards - shares forfeited (in dollars per share)	59
Weighted average grant date fair value of restricted stock awards - end of period (in dollars per share)	$ 61	$ 56
Summary of stock option plan activity [Roll Forward]
Options - beginning balance (in shares)	42,902,000
Granted (in shares)	9,275,000
Exercised (in shares)	(7,826,000)
Forfeited or expired (in shares)	(431,000)
Options - ending balance (in shares)	43,920,000	42,902,000
Options exercisable (in shares)	26,524,000
Additional disclosures pertaining to stock options [Abstract]
Weighted average exercise price of options - beginning of period (in dollars per share)	$ 52
Weighted average exercise price of options - shares granted (in dollars per share)	62
Weighted average exercise price of options - shares exercised (in dollars per share)	42
Weighted average exercise price of options - shares forfeited or expired (in dollars per share)	62
Weighted average exercise price of options - end of period (in dollars per share)	56	$ 52
Weighted average exercise price of options exercisable - end of period (in dollars per share)	$ 52
Weighted average remaining contractual life, options outstanding (in years)	4 years
Weighted average remaining contractual life, options exercisable (in years)	3 years
Value of unexercised in-the-money options, options outstanding	$ 485
Value of unexercised in-the-money options, options exercisable	402
Stock-based compensation, additional disclosures [Abstract]
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	55	$ 63	$ 51
Proceeds from Stock Options Exercised	$ 299	314	289
Incentive Stock Plans [Member]
Additional disclosures pertaining to stock based compensation [Abstract]
Number of shares available for grant (in shares)	11,554,000
Unrecognized compensation expense	$ 57
Unrecognized compensation expense, weighted-average period of recognition in years	2 years 1 month 6 days
Total fair value of shares vested	$ 70	71	69
Stock Option Plans [Member]
Additional disclosures pertaining to stock based compensation [Abstract]
Number of shares available for grant (in shares)	37,175,000
Unrecognized compensation expense	$ 44
Unrecognized compensation expense, weighted-average period of recognition in years	1 year 6 months
Stock-based compensation, additional disclosures [Abstract]
Contractual term (in years)	6 years
Vesting period (in years)	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 200	$ 211	$ 180
Program 2015 [Member]
Stock Repurchases [Abstract]
Stock Repurchase Program, Authorized Amount				$ 5,000