| Purchased Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified | Sep. 30, 2012 | Dec. 31, 2011 | 
|---|---|---|
| Acquired Finite-Lived Intangible Assets [Line Items] | ||
| Gross | $ 1,029.3 | $ 1,077.4 | 
| Accumulated Amortization | (541.7) | (527.2) | 
| Net | 487.6 | 550.2 | 
| Purchased Data Files [Member] | ||
| Acquired Finite-Lived Intangible Assets [Line Items] | ||
| Gross | 299.5 | 316.2 | 
| Accumulated Amortization | (237.1) | (240.5) | 
| Net | 62.4 | 75.7 | 
| Acquired Software and Technology [Member] | ||
| Acquired Finite-Lived Intangible Assets [Line Items] | ||
| Gross | 34.9 | 68.3 | 
| Accumulated Amortization | (12.7) | (41.1) | 
| Net | 22.2 | 27.2 | 
| Customer Relationships [Member] | ||
| Acquired Finite-Lived Intangible Assets [Line Items] | ||
| Gross | 519.7 | 518.2 | 
| Accumulated Amortization | (155.6) | (130.3) | 
| Net | 364.1 | 387.9 | 
| Proprietary Database [Member] | ||
| Acquired Finite-Lived Intangible Assets [Line Items] | ||
| Gross | 125.0 | 125.0 | 
| Accumulated Amortization | (110.9) | (95.5) | 
| Net | 14.1 | 29.5 | 
| Non-compete Agreements [Member] | ||
| Acquired Finite-Lived Intangible Assets [Line Items] | ||
| Gross | 9.2 | 9.0 | 
| Accumulated Amortization | (4.9) | (3.1) | 
| Net | 4.3 | 5.9 | 
| Trade Names and Other Intangible Assets [Member] | ||
| Acquired Finite-Lived Intangible Assets [Line Items] | ||
| Gross | 41.0 | 40.7 | 
| Accumulated Amortization | (20.5) | (16.7) | 
| Net | $ 20.5 | $ 24.0 |