Financing arrangements (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member]	Dec. 31, 2011 0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member]	Mar. 31, 2012 1.875% notes due 2014 (1.875% 2014 Notes) [Member]	Dec. 31, 2011 1.875% notes due 2014 (1.875% 2014 Notes) [Member]	Mar. 31, 2012 4.85% notes due 2014 (4.85% 2014 Notes) [Member]	Dec. 31, 2011 4.85% notes due 2014 (4.85% 2014 Notes) [Member]	Mar. 31, 2012 2.30% notes due 2016 (2.30% 2016 Notes) [Member]	Dec. 31, 2011 2.30% notes due 2016 (2.30% 2016 Notes) [Member]	Mar. 31, 2012 2.50% notes due 2016 (2.50% 2016 Notes) [Member]	Dec. 31, 2011 2.50% notes due 2016 (2.50% 2016 Notes) [Member]	Mar. 31, 2012 5.85% notes due 2017 (5.85% 2017 Notes) [Member]	Dec. 31, 2011 5.85% notes due 2017 (5.85% 2017 Notes) [Member]	Mar. 31, 2012 6.15% notes due 2018 (6.15% 2018 Notes) [Member]	Dec. 31, 2011 6.15% notes due 2018 (6.15% 2018 Notes) [Member]	Mar. 31, 2012 4.375% euro denominated notes due 2018 (4.375% 2018 euro Notes) [Member]	Dec. 31, 2011 4.375% euro denominated notes due 2018 (4.375% 2018 euro Notes) [Member]	Mar. 31, 2012 5.70% notes due 2019 (5.70% 2019 Notes) [Member]	Dec. 31, 2011 5.70% notes due 2019 (5.70% 2019 Notes) [Member]	Mar. 31, 2012 4.50% notes due 2020 (4.50% 2020 Notes) [Member]	Dec. 31, 2011 4.50% notes due 2020 (4.50% 2020 Notes) [Member]	Mar. 31, 2012 3.45% notes due 2020 (3.45% 2020 Notes) [Member]	Dec. 31, 2011 3.45% notes due 2020 (3.45% 2020 Notes) [Member]	Mar. 31, 2012 4.10% notes due 2021 (4.10% 2021 Notes) [Member]	Dec. 31, 2011 4.10% notes due 2021 (4.10% 2021 Notes) [Member]	Mar. 31, 2012 3.875% notes due 2021 (3.875% 2021 Notes) [Member]	Dec. 31, 2011 3.875% notes due 2021 (3.875% 2021 Notes) [Member]	Mar. 31, 2012 5.50% pound sterling denominated notes due 2026 (5.50% 2026 pound sterling Notes) [Member]	Dec. 31, 2011 5.50% pound sterling denominated notes due 2026 (5.50% 2026 pound sterling Notes) [Member]	Mar. 31, 2012 6.375% notes due 2037 (6.375% 2037 Notes) [Member]	Dec. 31, 2011 6.375% notes due 2037 (6.375% 2037 Notes) [Member]	Mar. 31, 2012 6.90% notes due 2038 (6.90% 2038 Notes) [Member]	Dec. 31, 2011 6.90% notes due 2038 (6.90% 2038 Notes) [Member]	Mar. 31, 2012 6.40% notes due 2039 (6.40% 2039 Notes) [Member]	Dec. 31, 2011 6.40% notes due 2039 (6.40% 2039 Notes) [Member]	Mar. 31, 2012 5.75% notes due 2040 (5.75% 2040 Notes) [Member]	Dec. 31, 2011 5.75% notes due 2040 (5.75% 2040 Notes) [Member]	Mar. 31, 2012 4.95% notes due 2041 (4.95% 2041 Notes) [Member]	Dec. 31, 2011 4.95% notes due 2041 (4.95% 2041 Notes) [Member]	Mar. 31, 2012 5.15% notes due 2041 (5.15% 2041 Notes) [Member]	Dec. 31, 2011 5.15% notes due 2041 (5.15% 2041 Notes) [Member]	Mar. 31, 2012 5.65% notes due 2042 (5.65% 2042 Notes) [Member]	Dec. 31, 2011 5.65% notes due 2042 (5.65% 2042 Notes) [Member]
Debt Instruments [Line Items]
Stated contractual interest rate on note			0.375%	0.375%	1.875%	1.875%	4.85%	4.85%	2.30%	2.30%	2.50%	2.50%	5.85%	5.85%	6.15%	6.15%	4.375%	4.375%	5.70%	5.70%	4.50%	4.50%	3.45%	3.45%	4.10%	4.10%	3.875%	3.875%	5.50%	5.50%	6.375%	6.375%	6.90%	6.90%	6.40%	6.40%	5.75%	5.75%	4.95%	4.95%	5.15%	5.15%	5.65%	5.65%
Financing arrangements (Textual) [Abstract]
Repayment of debt	$ 84	$ 2,500