Investments (Schedule Of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses And Fair Value Of Investments) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 4,012.0	$ 3,915.6
Fair value	4,344.9	4,147.5
Corporate Bonds Backed By The Federal Deposit Insurance Corporation [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4.3	48.7
Fair value	$ 4.3	$ 49.1

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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