Debt (Details)	3 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2013 USD ($)	Apr. 29, 2013 EUR (€)	Jun. 30, 2013 Commercial paper [Member] USD ($)	Jun. 30, 2013 Commercial paper [Member] USD ($)	Dec. 31, 2012 Commercial paper [Member] USD ($)	Apr. 15, 2013 4.250% Senior notes due 2042 [Member] USD ($)	Mar. 08, 2013 4.250% Senior notes due 2042 [Member] USD ($)	Dec. 31, 2012 4.250% Senior notes due 2042 [Member] USD ($)	May 21, 2013 4.45% notes due 2043 [Member] USD ($)
Debt Instrument
Total debt			$ 347,000,000	$ 347,000,000	$ 50,000,000
Weighted average commercial paper outstanding			358,000,000	261,000,000
Weighted-average interest rates (as a percent)			0.35%	0.37%
Face amount of debt						256,000,000	90,000,000		250,000,000
Stated interest rate						4.25%	4.25%		4.45%
Credit facility maximum borrowing amount		650,000,000
Short-term debt aggregate principal amount								166,000,000
Repayment of debt	$ 306,000,000