Investments of Insurance Subsidiaries - Schedule of Investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Available For Sale Securities [Line Items]
Amortized Cost	$ 552	$ 617
Unrealized Amounts, Gains	24	20
Unrealized Amounts, Losses	(6)	(9)
Fair Value	570	628
Amounts classified as current assets	(55)	(80)
Investment carrying value	515	548
Auction rate securities [Member]
Available For Sale Securities [Line Items]
Fair Value	68
Debt securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	550	610
Unrealized Amounts, Gains	23	19
Unrealized Amounts, Losses	(6)	(8)
Fair Value	567	621
Debt securities [Member] \| States and municipalities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	395	398
Unrealized Amounts, Gains	23	19
Unrealized Amounts, Losses
Fair Value	418	417
Debt securities [Member] \| Auction rate securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	74	139
Unrealized Amounts, Gains
Unrealized Amounts, Losses	(6)	(8)
Fair Value	68	131
Debt securities [Member] \| Asset-backed securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	14	20
Unrealized Amounts, Gains
Unrealized Amounts, Losses
Fair Value	14	20
Debt securities [Member] \| Money market funds [Member]
Available For Sale Securities [Line Items]
Amortized Cost	67	53
Unrealized Amounts, Gains
Unrealized Amounts, Losses
Fair Value	67	53
Equity securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	2	7
Unrealized Amounts, Gains	1	1
Unrealized Amounts, Losses		(1)
Fair Value	$ 3	$ 7

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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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

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

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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+ Details

- Definition

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 Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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