Location and Fair Values of Derivative Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Designated as Hedging Instrument | Other Long term Investments
Derivative [Line Items]
Asset Derivatives Fair Value	$ 111.9	$ 137.7
Designated as Hedging Instrument | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	174.3	173.7
Designated as Hedging Instrument | Interest Rate Swaps | Other Long term Investments
Derivative [Line Items]
Asset Derivatives Fair Value	109.0	134.2
Designated as Hedging Instrument | Interest Rate Swaps | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	31.2	32.9
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Long term Investments
Derivative [Line Items]
Asset Derivatives Fair Value	2.9	3.5
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	143.1	140.8
Not Designated as Hedging Instrument | Embedded Derivative in Modified Coinsurance Arrangement | Other Liability
Derivative [Line Items]
Liability Derivatives Fair Value	$ 123.4	$ 135.7