Stock-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended
	Feb. 29, 2012 Ratio	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense related to stock-based awards of subsidiaries		$ 2.0	$ 18.2
Expense related to stock-based awards			43.0	17.6
Common stock, stock split	1.742
Maximum number of shares of the Company's common stock			6,500,000
Option Exchange exercise price		$ 20.09
Replacement options exercise price		$ 8.22	$ 8.22
New vesting schedule on grant-by-grant basis		10
Percentage of Replacement Options immediately vested		20.00%
Number of installments vesting period		4
Percentage of remaining options vesting		20.00%
Number of anniversaries of exchange date		4 years
Return on investment		1.50%	1.50%
Average common stock closing price per share			$ 57.41
Number of trailing day of common stock			30 days
Eligible option to purchase common stock granted		290,334	290,334
Option Exchange, additional expenses			2.2
Additional option exchange expense will be recognized in future period			13.0
Vesting of Performance-Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Return on investment		1.50%	1.50%
Average common stock closing price per share			$ 57.41
Liability-classified awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense related to stock-based awards		1.8	17.3
Equity-classified awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense related to stock-based awards		0.2	0.9
2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, stock split	1.742
Shares issued with respect to incentive stock options		6,867,018	6,867,018
Stock appreciation and options rights granted to individual		3,433,509	3,433,509
Maximum number of shares of common stock which may be delivered pursuant to performance-based awards		1,373,404	1,373,404
Aggregate amount of compensation to be paid in respect of all performance-based awards			$ 25.0