Financing arrangements (Details 2) (USD $) In Millions, unless otherwise specified						12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Interest Rate Swap [Member]	Dec. 31, 2010 Interest Rate Swap [Member]	Dec. 31, 2011 Interest Rate Swap [Member] 5.85% notes due 2017 (5.85% 2017 Notes) [Member]	Dec. 31, 2010 Interest Rate Swap [Member] 5.85% notes due 2017 (5.85% 2017 Notes) [Member]	Dec. 31, 2011 Interest Rate Swap [Member] 4.85% notes due 2014 (4.85% 2014 Notes) [Member]	Dec. 31, 2010 Interest Rate Swap [Member] 4.85% notes due 2014 (4.85% 2014 Notes) [Member]	Dec. 31, 2011 Interest Rate Swap [Member] 5.70% notes due 2019 (5.70% 2019 Notes) [Member]	Dec. 31, 2010 Interest Rate Swap [Member] 5.70% notes due 2019 (5.70% 2019 Notes) [Member]	Dec. 31, 2011 Interest Rate Swap [Member] 6.15% notes due 2018 (6.15% 2018 Notes) [Member]	Dec. 31, 2010 Interest Rate Swap [Member] 6.15% notes due 2018 (6.15% 2018 Notes) [Member]
The effective interest rates on notes after giving effect to the related interest rate swap agreements and the notional amounts of interest rate swap agreements
Effective interest rate						LIBOR + 2.5%		LIBOR + 0.3%		LIBOR + 2.6%		LIBOR + 1.8%
Notional amount	$ 3,600	$ 3,600	$ 1,500	$ 3,600	$ 3,600	$ 1,100	$ 1,100	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 500	$ 500