Fair Value Of Financial Instruments (Narrative) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impact of including the nonperformance risk in valuation of pre-tax net insured derivative liability	$ 12	$ 11
Percentage of level 3 assets at fair value in total assets measured at fair value value	27.00%	21.00%
Percentage of level 3 liabilities at fair value in total liabilities measured at fair value	40.00%	37.00%

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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