Fair Value Measurements (Narrative) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net assets measured at fair value on a recurring basis	$ 2,300	$ 2,400
Net assets measured at fair value on a recurring basis measured using unobservable input and as Level 3	$ (2)	$ 7

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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