Acquisition-related charges (Details) (National [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		15 Months Ended	24 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		24 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012 Jobs	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]	Sep. 30, 2013 Amortization of intangible assets [Member]	Sep. 30, 2012 Amortization of intangible assets [Member]	Sep. 30, 2013 Amortization of intangible assets [Member]	Sep. 30, 2012 Amortization of intangible assets [Member]	Sep. 30, 2013 Retention bonuses [Member]	Sep. 30, 2012 Retention bonuses [Member]	Sep. 30, 2013 Retention bonuses [Member]	Sep. 30, 2012 Retention bonuses [Member]	Sep. 30, 2013 Severance and other benefits [Member]	Sep. 30, 2012 Severance and other benefits [Member]	Sep. 30, 2013 Severance and other benefits [Member]	Sep. 30, 2012 Severance and other benefits [Member]	Sep. 30, 2013 Severance and other benefits [Member]	Sep. 30, 2013 Stock-based compensation [Member]	Sep. 30, 2012 Stock-based compensation [Member]	Sep. 30, 2013 Stock-based compensation [Member]	Sep. 30, 2012 Stock-based compensation [Member]	Sep. 30, 2013 Transaction and other costs [Member]	Sep. 30, 2012 Transaction and other costs [Member]	Sep. 30, 2013 Transaction and other costs [Member]	Sep. 30, 2012 Transaction and other costs [Member]	Sep. 30, 2013 As recorded in Acquisition charges [Member]	Sep. 30, 2012 As recorded in Acquisition charges [Member]	Sep. 30, 2013 As recorded in Acquisition charges [Member]	Sep. 30, 2012 As recorded in Acquisition charges [Member]	Sep. 30, 2013 Distributor contract termination recorded in COR [Member]	Sep. 30, 2012 Distributor contract termination recorded in COR [Member]	Sep. 30, 2013 Distributor contract termination recorded in COR [Member]	Sep. 30, 2012 Distributor contract termination recorded in COR [Member]	Dec. 31, 2012 Distributor contract termination recorded in COR [Member]	Dec. 31, 2011 Distributor contract termination recorded in COR [Member] Distributors
Business Combination, Separately Recognized Transactions [Line Items]
Finite-Lived Intangible Asset, Useful Life						2 years	10 years
Acquisition-related costs	$ 86	$ 106	$ 257	$ 384				$ 81	$ 81	$ 244	$ 244	$ 2	$ 5	$ 5	$ 53	$ 0	$ 3	$ 0	$ 17	$ 86	$ 3	$ 4	$ 8	$ 14	$ 0	$ 13	$ 0	$ 35	$ 86	$ 106	$ 257	$ 363	$ 0	$ 0	$ 0	$ 21	$ 21
Number of jobs eliminated (in jobs)					350
Severance and other benefit costs paid related to business acquisition																				$ 82
Number of discontinued distributors																																						1