Quarterly Financial Data - Schedule of Quarterly Financial Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Total revenues	$ 3,521us-gaap_Revenues	$ 3,523us-gaap_Revenues	$ 3,593us-gaap_Revenues	$ 3,688us-gaap_Revenues	$ 3,782us-gaap_Revenues	$ 3,597us-gaap_Revenues	$ 3,616us-gaap_Revenues	$ 3,618us-gaap_Revenues	$ 14,325us-gaap_Revenues	$ 14,613us-gaap_Revenues	$ 14,072us-gaap_Revenues
Income from continuing operations	215	179	303	265	248	318	261	322	962	1,149	968
Income from continuing operations, Per share-basic	$ 0.58	$ 0.47	$ 0.79	$ 0.68					$ 2.52	$ 2.96	$ 2.45
Income from continuing operations, Per share-basic and diluted					$ 0.64	$ 0.82	$ 0.67	$ 0.82
Income from continuing operations, Per share-diluted	$ 0.57	$ 0.47	$ 0.79	$ 0.68					$ 2.52	$ 2.95	$ 2.44
Discontinued operations, net	(7)	29	(187)	(206)	(446)	(36)	8	(80)	(371)	(554)	(400)
Discontinued operations, net, Per share-basic and diluted	$ (0.02)	$ 0.08	$ (0.49)	$ (0.53)	$ (1.15)	$ (0.09)	$ 0.02	$ (0.20)
Net income	$ 208us-gaap_NetIncomeLoss	$ 208us-gaap_NetIncomeLoss	$ 116us-gaap_NetIncomeLoss	$ 59us-gaap_NetIncomeLoss	$ (198)us-gaap_NetIncomeLoss	$ 282us-gaap_NetIncomeLoss	$ 269us-gaap_NetIncomeLoss	$ 242us-gaap_NetIncomeLoss	$ 591us-gaap_NetIncomeLoss	$ 595us-gaap_NetIncomeLoss	$ 568us-gaap_NetIncomeLoss
Per share-basic	$ 0.56us-gaap_EarningsPerShareBasic	$ 0.55us-gaap_EarningsPerShareBasic	$ 0.30us-gaap_EarningsPerShareBasic	$ 0.15us-gaap_EarningsPerShareBasic					$ 1.55us-gaap_EarningsPerShareBasic	$ 1.53us-gaap_EarningsPerShareBasic	$ 1.44us-gaap_EarningsPerShareBasic
Per share-basic and diluted					$ (0.51)us-gaap_EarningsPerShareBasicAndDiluted	$ 0.73us-gaap_EarningsPerShareBasicAndDiluted	$ 0.69us-gaap_EarningsPerShareBasicAndDiluted	$ 0.62us-gaap_EarningsPerShareBasicAndDiluted
Per share-diluted	$ 0.55us-gaap_EarningsPerShareDiluted	$ 0.55us-gaap_EarningsPerShareDiluted	$ 0.30us-gaap_EarningsPerShareDiluted	$ 0.15us-gaap_EarningsPerShareDiluted					$ 1.55us-gaap_EarningsPerShareDiluted	$ 1.53us-gaap_EarningsPerShareDiluted	$ 1.43us-gaap_EarningsPerShareDiluted

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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The amount of net income (loss) from continuing operations per each basic and diluted share of common stock or unit when the per share amount is the same for both basic and diluted shares.

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The amount of net income (loss) from continuing operations per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) derived from continuing operations during the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Per basic and diluted share amount, after tax, of income (loss) from the day-to-day business activities of the discontinued operation and gain (loss) from the disposal of the discontinued operation, when the per share amount is the same.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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