Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Stock-based compensation awards
Required minimum age of a participant upon separation from service to meet the criteria for Long Service Separation (in years)	55 years
Minimum term of service to meet criteria for Long Service Separation (in years)	5 years
Term life of SARs and option awards (in years)	10 years
Term life of vested options/SARs from separation date (in years)			5 years
Stock-based compensation expense, before tax (in dollars)	$ 101	$ 135
Assumptions used in determining the fair value of the stock-based awards
Weighted-average dividend yield (as a percent)	3.23%	2.27%
Weighted-average volatility (as a percent)	31.10%	28.40%
Volatilities, low end of range (as a percent)	22.50%	19.90%
Volatilities, high end of range (as a percent)	33.40%	35.90%
Risk-free interest rates, low end of range (as a percent)	0.62%	0.22%
Risk-free interest rates, high end of range (as a percent)	1.73%	2.08%
Weighted-average expected lives (in years)	8 years	8 years
Unrecognized compensation cost related to nonvested stock-based compensation awards (in dollars)	$ 308
Term of amortization of unrecognized compensation cost over weighted-average remaining requisite service periods (in years)	2 years 2 months
Stock Options
Stock-based compensation awards
Shares Granted (in shares)	4,243,272	7,939,497
Weighted-Average Fair Value Per Share (in dollars per share)	$ 20.64	$ 23.61
Share-based Compensation Arrangement by Share-based Payment Award Grant Date Price Per Share	74.77	83.34
RSUs
Stock-based compensation awards
Share-based Compensation Arrangement by Share-based Payment Award Grant Date Price Per Share	$ 74.77	$ 83.02
Shares Granted (in shares)	1,085,505	1,690,661
Weighted-Average Fair Value Per Share (in dollars per share)	$ 68.04	$ 77.55
PRSUs
Stock-based compensation awards
Share-based Compensation Arrangement by Share-based Payment Award Grant Date Price Per Share	$ 74.77	$ 82.90
Shares Granted (in shares)	614,347	132,068
Weighted-Average Fair Value Per Share (in dollars per share)	$ 64.71	$ 77.47
Grants prior to 2015
Stock-based compensation awards
Vesting period of awards, after the date of grant (in years)	3 years
2015 and 2016 Grants
Stock-based compensation awards
Graded vesting period of awards granted (in years)	3 years
2015 and 2016 Grants | PRSUs
Stock-based compensation awards
Vesting period of awards, after the date of grant (in years)	3 years