Description of business and significant accounting policies and practices (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Reportable_Segments	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Reportable segments			2
Basic EPS:
Net income	$ 826	$ 629	$ 1,996	$ 1,651
Income allocated to RSUs	(13)	(11)	(31)	(29)
Income allocated to common stock for basic EPS calculation	813	618	1,965	1,622
Weighted average number of shares outstanding, basic (in shares)	1,060	1,096	1,070	1,102
Basic EPS (in dollars per share)	$ 0.77	$ 0.56	$ 1.84	$ 1.47
Adjustment for dilutive shares:
Stock-based compensation plans (in shares)	14	15	15	15
Diluted EPS:
Net income	826	629	1,996	1,651
Income allocated to RSUs	(13)	(11)	(31)	(28)
Income allocated to common stock for diluted EPS calculation	$ 813	$ 618	$ 1,965	$ 1,623
Weighted average number of shares outstanding, diluted (in shares)	1,074	1,111	1,085	1,117
Diluted EPS (in dollars per share)	$ 0.76	$ 0.56	$ 1.81	$ 1.45
Antidilutive securities excluded from computation of earnings per share, Amount (in shares)	11	0	11	0