Investments - Available-For-Sale Securities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Asset-backed and mortgage-backed securities impairment	$ 1.6
Asset-backed securities and collateralized mortgage obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Commercial paper secured by mortgaged-backed securities	$ 5.6
Maximum [Member] \| Commercial paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, maturities	1 year
Maximum [Member] \| Asset-backed securities and collateralized mortgage obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, maturities	26 years

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant