Fair Value Measurements - Measured on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Derivatives	$ 23	$ 27
Liabilities
Derivatives	106	85
Equity securities
Assets
Fair value of investments measured on recurring basis	39	79
Mutual funds
Assets
Fair value of investments measured on recurring basis	917	856
U.S. Government securities
Assets
Fair value of investments measured on recurring basis	116	113
Other securities
Assets
Fair value of investments measured on recurring basis	170	151
Other commingled funds
Liabilities
Assets measured at NAV	19	0
Level 1
Assets
Derivatives	0	0
Liabilities
Derivatives	0	0
Level 1 \| Equity securities
Assets
Fair value of investments measured on recurring basis	39	79
Level 1 \| Mutual funds
Assets
Fair value of investments measured on recurring basis	917	856
Level 1 \| U.S. Government securities
Assets
Fair value of investments measured on recurring basis	0	0
Level 1 \| Other securities
Assets
Fair value of investments measured on recurring basis	0	0
Level 2
Assets
Derivatives	23	27
Liabilities
Derivatives	106	85
Level 2 \| Equity securities
Assets
Fair value of investments measured on recurring basis	0	0
Level 2 \| Mutual funds
Assets
Fair value of investments measured on recurring basis	0	0
Level 2 \| U.S. Government securities
Assets
Fair value of investments measured on recurring basis	116	113
Level 2 \| Other securities
Assets
Fair value of investments measured on recurring basis	$ 170	$ 151

Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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