Available-for-sale investments (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair values of available-for-sale debt security investments by contractual maturity
Maturing in one year or less	$ 10,820	$ 7,175
Maturing after one year through three years	4,671	5,014
Maturing after three years through five years	5,742	6,286
Maturing after five years through ten years	1,432	1,620
Mortgage- and asset-backed securities	2,849	3,596
Total available-for-sale investments	25,605	23,745
Total interest-bearing securities [Member]
Fair values of available-for-sale debt security investments by contractual maturity
Total available-for-sale investments	$ 25,514	$ 23,691