Description of business and significant accounting policies and practices (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Reportable_Segments	Jun. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Reportable segments			2
Basic EPS:
Net income	$ 683	$ 660	$ 1,170	$ 1,022
Income allocated to RSUs	(10)	(11)	(18)	(18)
Income allocated to common stock for basic EPS calculation	673	649	1,152	1,004
Weighted average number of shares outstanding, basic (in shares)	1,071	1,103	1,076	1,105
Basic EPS (in dollars per share)	$ 0.63	$ 0.59	$ 1.07	$ 0.91
Adjustment for dilutive shares:
Stock-based compensation plans (in shares)	15	14	15	15
Diluted EPS:
Net income	683	660	1,170	1,022
Income allocated to RSUs	(10)	(11)	(18)	(18)
Income allocated to common stock for diluted EPS calculation	$ 673	$ 649	$ 1,152	$ 1,004
Weighted average number of shares outstanding, diluted (in shares)	1,086	1,117	1,091	1,120
Diluted EPS (in dollars per share)	$ 0.62	$ 0.58	$ 1.06	$ 0.90
Antidilutive securities excluded from computation of earnings per share, Amount (in shares)	14	13	12	23