Location and Fair Values of Derivative Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Designated as Hedging Instrument | Other Long term Investments
Derivative [Line Items]
Asset Derivatives Fair Value	$ 137.7	$ 99.1
Designated as Hedging Instrument | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	173.7	199.6
Designated as Hedging Instrument | Interest Rate Swaps | Other Long term Investments
Derivative [Line Items]
Asset Derivatives Fair Value	134.2	98.4
Designated as Hedging Instrument | Interest Rate Swaps | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	32.9	39.1
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Long term Investments
Derivative [Line Items]
Asset Derivatives Fair Value	3.5	0.7
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	140.8	160.5
Not Designated as Hedging Instrument | Embedded Derivative in Modified Coinsurance Arrangement | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	$ 135.7	$ 96.3