Summary of Capped Call (Equity Options) Issued (Detail) (Capped call (equity options), USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	6 Months Ended
	Nov. 30, 2010	Jun. 30, 2012
Option Indexed to Issuer's Equity [Line Items]
Original Number of Options	8,430,000	8,433,123
Net Premium Paid	$ 50.3	$ 50.3
Series I
Option Indexed to Issuer's Equity [Line Items]
Original Number of Options		2,811,041
Net Premium Paid		16.8
Series II
Option Indexed to Issuer's Equity [Line Items]
Original Number of Options		2,811,041
Net Premium Paid		16.8
Series III
Option Indexed to Issuer's Equity [Line Items]
Original Number of Options		2,811,041
Net Premium Paid		$ 16.7
Minimum
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 74.54
Minimum | Series I
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 74.54
Minimum | Series II
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 74.54
Minimum | Series III
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 74.54
Maximum
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 97.35
Maximum | Series I
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 97.35
Maximum | Series II
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 97.35
Maximum | Series III
Option Indexed to Issuer's Equity [Line Items]
Adjusted Strike Price		$ 97.35