| Debt Outstanding (Detail) (USD $) In Millions, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012 | 
|---|---|---|
| Debt Outstanding [Line Items] | ||
| Total debt | $ 1,438.8 | $ 1,720.4 | 
| Less short-term debt and current maturities | (16.4) | (283.3) | 
| Less unamortized discounts | (2.2) | (2.3) | 
| Plus fair value adjustments | 7.6 | 12.6 | 
| Total long-term debt, net | 1,427.8 | 1,447.4 | 
| Commercial Paper [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 0 | 265.0 | 
| Notes, 7.34%, due in installments through May 2014 [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 15.0 | 30.0 | 
| Notes, 4.45%, due December 2014 [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 275.0 | 275.0 | 
| Notes, 6.30%, due July 2017 [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 272.5 | 272.5 | 
| Notes, 3.30%, due Dec 2022 [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 500.0 | 500.0 | 
| Debentures, 6.90%, Due July 2028 [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 125.0 | 125.0 | 
| Notes, 7.00%, Due July 2037 [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 250.0 | 250.0 | 
| Capitalized Lease Obligation [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | 0 | 2.2 | 
| Other [Member] | ||
| Debt Outstanding [Line Items] | ||
| Total debt | $ 1.3 | $ 0.7 |