Stock-based compensation (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Restricted Stock Units [Member]	Dec. 31, 2012 Restricted Stock Units [Member]	Dec. 31, 2011 Restricted Stock Units [Member]	Dec. 31, 2013 Stock Options [Member]	Dec. 31, 2012 Stock Options [Member]	Dec. 31, 2011 Stock Options [Member]	Dec. 31, 2013 Stock Option and Restricted Stock Units [Member]	Dec. 31, 2013 Performance Units [Member]	Dec. 31, 2012 Performance Units [Member]	Dec. 31, 2011 Performance Units [Member]	Dec. 31, 2012 Granted Prior to April 25, 2011 [Member] Restricted Stock Units [Member]	Dec. 31, 2011 Granted Prior to April 25, 2011 [Member] Restricted Stock Units [Member]	Dec. 31, 2011 Granted Prior to April 25, 2011 [Member] Stock Options [Member]	Dec. 31, 2010 Granted Prior to April 25, 2011 [Member] Stock Options [Member]	Dec. 31, 2013 Granted on April 25, 2011 through April 26, 2012 [Member] Restricted Stock Units [Member]	Dec. 31, 2013 Granted on and After April 26, 2010 [Member] Stock Options [Member]	Dec. 31, 2012 Granted on and After April 26, 2010 [Member] Stock Options [Member]	Dec. 31, 2011 Granted on and After April 26, 2010 [Member] Stock Options [Member]	Dec. 31, 2009 Granted Prior to April 26, 2010 [Member] Stock Options [Member]	May 22, 2013 the Amended 2009 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized for issuance																							104,000,000
Amount by which the pool of available shares will be reduced for each stock option granted	1	1	1
The number of shares by which the pool of available shares will be reduced for other types of awards granted				1.9	1.9	1.9					1.9	1.9	1.9
The amount of common stock available under the plan for future grants and/or issuances (in shares)	58,000,000
Period over which the grants of equity instruments vest											3 years	3 years	3 years	4 years	4 years	4 years	4 years
Description of vesting of restricted stock units and stock options	Stock options and RSUs granted on and after April 25, 2011, generally vest in approximately equal amounts on the second, third and fourth anniversaries of the grant date.
Expected dividend yield							2.20%	2.10%	2.00%									2.00%
Weighted-average risk-free interest rate							1.70%	1.60%	2.50%		0.40%	0.50%	1.20%					1.00%
Weighted average grant date fair value, granted (in usd per share)				$ 107.01	$ 72.99	$ 51.83					$ 102.73	$ 78.21	$ 49.50
Total fair value of units that vested during the year				$ 145	$ 139	$ 176					$ 270	$ 100	$ 25
Total unrecognized compensation cost related to nonvested awards										394	173
Weighted average number of years over which compensation cost related to nonvested awards is expected to be recognized										1 year 9 months 18 days	10 months 24 days
Expiration period of stock options from date of grant																			10 years	10 years	10 years	7 years
Total intrinsic value of stock options exercised during the year							210	320	47
Actual tax benefits realized from tax deductions from option exercises	$ 77	$ 117	$ 14
Units outstanding (in shares)				8,800,000	9,400,000						6,600,000	5,800,000
Weighted average grant date fair value of units, outstanding											$ 76.95	$ 65.15
Units granted (in shares)				2,800,000							2,100,000
Units, vested (in shares)				2,700,000							2,400,000
Weighted average grant date fair value, vested (in usd per share)				$ 54.74							$ 49.33
Units, forfeited (in shares)				700,000							500,000
Weighted average grant date fair value, forfeited (in usd per share)				$ 69.84							$ 73.13
Number of common shares issued for each performance unit earned	1	1	1