Investments of Insurance Subsidiaries - Schedule of Investments (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	$ 455		$ 462
Unrealized Amounts, Gains	23		21
Unrealized Amounts, Losses	(1)		(1)
Fair Value	477	$ 482	482
Amounts classified as current assets	(52)	(50)	(50)
Investment carrying value	425	432	432
Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	454		462
Unrealized Amounts, Gains	20		17
Unrealized Amounts, Losses	(1)		(1)
Fair Value	473	478	478
Debt Securities [Member] \| States and Municipalities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	415		428
Unrealized Amounts, Gains	20		17
Unrealized Amounts, Losses	(1)		(1)
Fair Value	434	444	444
Debt Securities [Member] \| Money Market Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	39		34
Fair Value	39	34	34
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	1
Unrealized Amounts, Gains	3		4
Fair Value	$ 4	$ 4	$ 4

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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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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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