Description of business and significant accounting policies and practices (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Reportable_Segments	Mar. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Reportable segments	2
Basic EPS:
Net income	$ 487	$ 362
Income allocated to RSUs	(7)	(7)
Income allocated to common stock for basic EPS calculation	480	355
Weighted average number of shares outstanding, basic (in shares)	1,081	1,107
Basic EPS (in dollars per share)	$ 0.44	$ 0.32
Adjustment for dilutive shares:
Stock-based compensation plans (in shares)	15	16
Diluted EPS:
Net income	487	362
Income allocated to RSUs	(7)	(7)
Income allocated to common stock for diluted EPS calculation	$ 480	$ 355
Weighted average number of shares outstanding, diluted (in shares)	1,096	1,123
Diluted EPS (in dollars per share)	$ 0.44	$ 0.32
Antidilutive securities excluded from computation of earnings per share, Amount (in shares)	10	31