Investments of Insurance Subsidiaries - Schedule of Investments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Available For Sale Securities [Line Items]
Amortized Cost	$ 454	$ 552
Unrealized Amounts, Gains	13	24
Unrealized Amounts, Losses	(2)	(6)
Fair Value	465	570
Amounts classified as current assets	(63)	(55)
Investment carrying value	402	515
Debt Securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	452	550
Unrealized Amounts, Gains	12	23
Unrealized Amounts, Losses	(2)	(6)
Fair Value	462	567
Debt Securities [Member] \| States and Municipalities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	383	395
Unrealized Amounts, Gains	12	23
Unrealized Amounts, Losses	(2)
Fair Value	393	418
Debt Securities [Member] \| Auction Rate Securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	32	74
Unrealized Amounts, Gains
Unrealized Amounts, Losses		(6)
Fair Value	32	68
Debt Securities [Member] \| Asset-Backed Securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	13	14
Unrealized Amounts, Gains
Unrealized Amounts, Losses
Fair Value	13	14
Debt Securities [Member] \| Money Market Funds [Member]
Available For Sale Securities [Line Items]
Amortized Cost	24	67
Unrealized Amounts, Gains
Unrealized Amounts, Losses
Fair Value	24	67
Equity Securities [Member]
Available For Sale Securities [Line Items]
Amortized Cost	2	2
Unrealized Amounts, Gains	1	1
Unrealized Amounts, Losses
Fair Value	$ 3	$ 3

- 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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