Financing arrangements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Carrying values of long-term borrowings
Other notes	$ 112	$ 109
Total debt	23,892	26,529
Less current portion	(7)	(2,495)
Total noncurrent debt	23,885	24,034
0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	0.375%	0.375%
Carrying values of long-term borrowings
Convertible notes, current	0	2,488
1.875% notes due 2014 (1.875% 2014 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	1.875%	1.875%
Carrying values of long-term borrowings
Total noncurrent debt	1,000	1,000
4.85% notes due 2014 (4.85% 2014 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	4.85%	4.85%
Carrying values of long-term borrowings
Total noncurrent debt	1,000	1,000
2.30% notes due 2016 (2.30% 2016 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	2.30%	2.30%
Carrying values of long-term borrowings
Total noncurrent debt	749	749
2.50% notes due 2016 (2.50% 2016 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	2.50%	2.50%
Carrying values of long-term borrowings
Total noncurrent debt	999	999
2.125% notes due 2017 (2.125% 2017 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	2.125%	2.125%
Carrying values of long-term borrowings
Total noncurrent debt	1,248	1,248
5.85% notes due 2017 (5.85% 2017 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	5.85%	5.85%
Carrying values of long-term borrowings
Total noncurrent debt	1,099	1,099
6.15% notes due 2018 (6.15% 2018 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	6.15%	6.15%
Carrying values of long-term borrowings
Total noncurrent debt	499	499
4.375% euro denominated notes due 2018 (4.375% 2018 euro Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	4.375%	4.375%
Carrying values of long-term borrowings
Total noncurrent debt	708	723
5.70% notes due 2019 (5.70% 2019 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	5.70%	5.70%
Carrying values of long-term borrowings
Total noncurrent debt	999	999
2.125% euro denominated notes due 2019 (2.125% 2019 euro Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	2.125%	2.125%
Carrying values of long-term borrowings
Total noncurrent debt	868	887
4.50% notes due 2020 (4.50% 2020 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	4.50%	4.50%
Carrying values of long-term borrowings
Total noncurrent debt	300	300
3.45% notes due 2020 (3.45% 2020 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	3.45%	3.45%
Carrying values of long-term borrowings
Total noncurrent debt	897	897
4.10% notes due 2021 (4.10% 2021 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	4.10%	4.10%
Carrying values of long-term borrowings
Total noncurrent debt	998	998
3.875% notes due 2021 (3.875% 2021 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	3.875%	3.875%
Carrying values of long-term borrowings
Total noncurrent debt	1,745	1,745
3.625% notes due 2022 (3.625% 2022 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	3.625%	3.625%
Carrying values of long-term borrowings
Total noncurrent debt	747	747
5.50% pound sterling denominated notes due 2026 (5.50% 2026 pound sterling Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	5.50%	5.50%
Carrying values of long-term borrowings
Total noncurrent debt	715	763
4.00% pound sterling denominated notes due 2029 (4.00% 2029 pound sterling Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	4.00%	4.00%
Carrying values of long-term borrowings
Total noncurrent debt	1,047	1,117
6.375% notes due 2037 (6.375% 2037 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	6.375%	6.375%
Carrying values of long-term borrowings
Total noncurrent debt	899	899
6.90% notes due 2038 (6.90% 2038 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	6.90%	6.90%
Carrying values of long-term borrowings
Total noncurrent debt	499	499
6.40% notes due 2039 (6.40% 2039 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	6.40%	6.40%
Carrying values of long-term borrowings
Total noncurrent debt	996	996
5.75% notes due 2040 (5.75% 2040 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	5.75%	5.75%
Carrying values of long-term borrowings
Total noncurrent debt	697	697
4.95% notes due 2041 (4.95% 2041 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	4.95%	4.95%
Carrying values of long-term borrowings
Total noncurrent debt	595	595
5.15% notes due 2041 (5.15% 2041 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	5.15%	5.15%
Carrying values of long-term borrowings
Total noncurrent debt	2,232	2,232
5.65% notes due 2042 (5.65% 2042 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	5.65%	5.65%
Carrying values of long-term borrowings
Total noncurrent debt	1,244	1,244
5.375% notes due 2043 (5.375% 2043 Notes) [Member]
Debt Instruments [Line Items]
Interest rate, stated percentage	5.375%	5.375%
Carrying values of long-term borrowings
Total noncurrent debt	$ 1,000	$ 1,000