Fair Value of Financial Assets and Liabilities Contractual Maturities of Investments (Detail) (Debt Securities, USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Debt Securities
Amortized Cost Basis
Due within one year	$ 1,651,057
Due after 1 year through 5 years	4,346,582
Due after 5 years through 10 years	429,524
Due after 10 years	344,428
Available For Sale Securities Amortized Cost	6,771,591	6,228,479
Aggregate Fair Value
Due within one year	1,654,507
Due after 1 year through 5 years	4,367,732
Due after 5 years through 10 years	446,114
Due after 10 years	340,952
Available For Sale Securities Fair Value	$ 6,809,305	$ 6,247,092

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

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