Shareholders' Equity and Dividend Availability (details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Apr. 30, 2015	May. 31, 2013
Shareholders' Equity and Dividend Availability disclosure
Number of authorized shares	1,755.0				1,755.0
Number of authorized shares, voting common stock	1,745.0				1,745.0
Number of authorized shares, preferred shares	5.0				5.0			5.0
Number of authorized shares, undesignated shares	5.0				5.0
Additional share repurchase authorization							$ 5,000
Number of shares purchased (in shares)	8.8	7.3	7.9	5.6	29.6
Cost of shares repurchased	$ 1,000	$ 750	$ 800	$ 600	$ 3,150
Average price paid per share	$ 113.47	$ 102.81	$ 101.62	$ 106.97	$ 106.46
Remaining capacity under share repurchase authorization	$ 3,334	$ 4,334	$ 5,084	$ 884	$ 3,334
Shares acquired to cover tax withholding costs and exercise costs					$ 74	$ 58