Investments of Insurance Subsidiaries - Schedule of Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	$ 443	$ 539
Unrealized Amounts, Gains	18	20
Unrealized Amounts, Losses	(1)	(1)
Fair Value	460	558
Amounts classified as current assets	(51)	(64)
Investment carrying value	409	494
Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	442	538
Unrealized Amounts, Gains	16	18
Unrealized Amounts, Losses	(1)	(1)
Fair Value	457	555
Debt Securities [Member] \| States and Municipalities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	429	477
Unrealized Amounts, Gains	16	18
Unrealized Amounts, Losses	(1)	(1)
Fair Value	444	494
Debt Securities [Member] \| Money Market Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	13	61
Fair Value	13	61
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	1	1
Unrealized Amounts, Gains	2	2
Fair Value	$ 3	$ 3

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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.

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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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